diff --git a/activerecord/lib/active_record/connection_adapters.rb b/activerecord/lib/active_record/connection_adapters.rb
index d4be1c084de..96b7078825c 100644
--- a/activerecord/lib/active_record/connection_adapters.rb
+++ b/activerecord/lib/active_record/connection_adapters.rb
@@ -31,6 +31,62 @@ module ActiveRecord
         class_name, path_to_adapter = @adapters[adapter_name.to_s]
 
         unless class_name
+          # To provide better error messages for adapters expecting the pre-7.2 adapter registration API, we attempt
+          # to load the adapter file from the old location which was required by convention, and then raise an error
+          # describing how to upgrade the adapter to the new API.
+          legacy_adapter_path = "active_record/connection_adapters/#{adapter_name}_adapter"
+          legacy_adapter_connection_method_name = "#{adapter_name}_connection".to_sym
+
+          begin
+            require legacy_adapter_path
+            # If we reach here it means we found the found a file that may be the legacy adapter and should raise.
+            if ActiveRecord::ConnectionHandling.method_defined?(legacy_adapter_connection_method_name)
+              # If we find the connection method then we care certain it is a legacy adapter.
+              deprecation_message = <<~MSG.squish
+                Database configuration specifies '#{adapter_name}' adapter but that adapter has not been registered.
+                Rails 7.2 has changed the way Active Record database adapters are loaded. The adapter needs to be
+                updated to register itself rather than being loaded by convention.
+                Ensure that the adapter in the Gemfile is at the latest version. If it is, then the adapter may need to
+                be modified.
+                See:
+                https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters.html#method-c-register
+              MSG
+
+              exception_message = <<~MSG.squish
+                Database configuration specifies '#{adapter_name}' adapter but that adapter has not been registered.
+                Ensure that the adapter in the Gemfile is at the latest version. If it is, then the adapter may need to
+                be modified.
+              MSG
+            else
+              # If we do not find the connection method we are much less certain it is a legacy adapter. Even though the
+              # file exists in the location defined by convenntion, it does not necessarily mean that file is supposed
+              # to define the adapter the legacy way. So raise an error that explains both possibilities.
+              deprecation_message = <<~MSG.squish
+                Database configuration specifies nonexistent '#{adapter_name}' adapter.
+                Available adapters are: #{@adapters.keys.sort.join(", ")}.
+                Ensure that the adapter is spelled correctly in config/database.yml and that you've added the necessary
+                adapter gem to your Gemfile if it's not in the list of available adapters.
+                Rails 7.2 has changed the way Active Record database adapters are loaded. Ensure that the adapter in
+                the Gemfile is at the latest version. If it is up to date, the adapter may need to be modified.
+                See:
+                https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters.html#method-c-register
+              MSG
+
+              exception_message = <<~MSG.squish
+                Database configuration specifies nonexistent '#{adapter_name}' adapter.
+                Available adapters are: #{@adapters.keys.sort.join(", ")}.
+                Ensure that the adapter is spelled correctly in config/database.yml and that you've added the necessary
+                adapter gem to your Gemfile and that it is at its latest version. If it is up to date, the adapter may
+                need to be modified.
+              MSG
+            end
+
+            ActiveRecord.deprecator.warn(deprecation_message)
+            raise AdapterNotFound, exception_message
+          rescue LoadError => error
+            # The adapter was not found in the legacy location so fall through to the error handling for a missing adapter.
+          end
+
           raise AdapterNotFound, <<~MSG.squish
             Database configuration specifies nonexistent '#{adapter_name}' adapter.
             Available adapters are: #{@adapters.keys.sort.join(", ")}.
diff --git a/activerecord/test/active_record/connection_adapters/fake_legacy_adapter.rb b/activerecord/test/active_record/connection_adapters/fake_legacy_adapter.rb
new file mode 100644
index 00000000000..6d4181ceda3
--- /dev/null
+++ b/activerecord/test/active_record/connection_adapters/fake_legacy_adapter.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionHandling
+    def fake_legacy_connection(config)
+      ConnectionAdapters::FakeLegacyAdapter.new nil, logger
+    end
+  end
+
+  module ConnectionAdapters
+    class FakeLegacyAdapter < AbstractAdapter
+      def active?
+        true
+      end
+    end
+  end
+end
diff --git a/activerecord/test/active_record/connection_adapters/fake_misleading_legacy_adapter.rb b/activerecord/test/active_record/connection_adapters/fake_misleading_legacy_adapter.rb
new file mode 100644
index 00000000000..093a1f50c5e
--- /dev/null
+++ b/activerecord/test/active_record/connection_adapters/fake_misleading_legacy_adapter.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    class FakeMisleadingLegacyAdapter < AbstractAdapter
+    end
+  end
+end
diff --git a/activerecord/test/cases/connection_adapters/registration_test.rb b/activerecord/test/cases/connection_adapters/registration_test.rb
index fc252ed996d..53bbefd3df1 100644
--- a/activerecord/test/cases/connection_adapters/registration_test.rb
+++ b/activerecord/test/cases/connection_adapters/registration_test.rb
@@ -16,34 +16,92 @@ module ActiveRecord
       end
 
       test "#register registers a new database adapter and #resolve can find it and raises if it cannot" do
-        assert_raises(ActiveRecord::AdapterNotFound) do
+        exception = assert_raises(ActiveRecord::AdapterNotFound) do
           ActiveRecord::ConnectionAdapters.resolve("fake")
         end
 
+        assert_match(
+          /Database configuration specifies nonexistent 'fake' adapter. Available adapters are:/,
+          exception.message
+        )
+
         ActiveRecord::ConnectionAdapters.register("fake", "FakeActiveRecordAdapter", @fake_adapter_path)
 
         assert_equal "FakeActiveRecordAdapter", ActiveRecord::ConnectionAdapters.resolve("fake").name
       end
 
       test "#register allows for symbol key" do
-        assert_raises(ActiveRecord::AdapterNotFound) do
+        exception = assert_raises(ActiveRecord::AdapterNotFound) do
           ActiveRecord::ConnectionAdapters.resolve("fake")
         end
 
+        assert_match(
+          /Database configuration specifies nonexistent 'fake' adapter. Available adapters are:/,
+          exception.message
+        )
+
         ActiveRecord::ConnectionAdapters.register(:fake, "FakeActiveRecordAdapter", @fake_adapter_path)
 
         assert_equal "FakeActiveRecordAdapter", ActiveRecord::ConnectionAdapters.resolve("fake").name
       end
 
       test "#resolve allows for symbol key" do
-        assert_raises(ActiveRecord::AdapterNotFound) do
+        exception = assert_raises(ActiveRecord::AdapterNotFound) do
           ActiveRecord::ConnectionAdapters.resolve("fake")
         end
 
+        assert_match(
+          /Database configuration specifies nonexistent 'fake' adapter. Available adapters are:/,
+          exception.message
+        )
+
         ActiveRecord::ConnectionAdapters.register("fake", "FakeActiveRecordAdapter", @fake_adapter_path)
 
         assert_equal "FakeActiveRecordAdapter", ActiveRecord::ConnectionAdapters.resolve(:fake).name
       end
     end
+
+    class RegistrationIsolatedTest < ActiveRecord::TestCase
+      include ActiveSupport::Testing::Isolation
+
+      def setup
+        @original_adapters = ActiveRecord::ConnectionAdapters.instance_variable_get(:@adapters).dup
+      end
+
+      test "#resolve raises if the adapter is using the pre 7.2 adapter registration API" do
+        exception = assert_raises(ActiveRecord::AdapterNotFound) do
+          assert_deprecated(ActiveRecord.deprecator) do
+            ActiveRecord::ConnectionAdapters.resolve("fake_legacy")
+          end
+        end
+
+        assert_match(
+          /Database configuration specifies 'fake_legacy' adapter but that adapter has not been registered. Ensure that the adapter in the Gemfile is at the latest version. If it is, then the adapter may need to be modified./,
+          exception.message
+        )
+      ensure
+        ActiveRecord::ConnectionAdapters.instance_variable_get(:@adapters).delete("fake_legacy")
+      end
+
+      test "#resolve raises if the adapter maybe is using the pre 7.2 adapter registration API but we are not sure" do
+        exception = assert_raises(ActiveRecord::AdapterNotFound) do
+          assert_deprecated(ActiveRecord.deprecator) do
+            ActiveRecord::ConnectionAdapters.resolve("fake_misleading_legacy")
+          end
+        end
+
+        assert_match(
+          /Database configuration specifies nonexistent 'fake_misleading_legacy' adapter. Available adapters are:/,
+          exception.message
+        )
+
+        assert_match(
+          /Ensure that the adapter is spelled correctly in config\/database.yml and that you've added the necessary adapter gem to your Gemfile and that it is at its latest version. If it is up to date, the adapter may need to be modified./,
+          exception.message
+        )
+      ensure
+        ActiveRecord::ConnectionAdapters.instance_variable_get(:@adapters).delete("fake_misleading_legacy")
+      end
+    end
   end
 end