Docs: in typical usage, "descendant" is the noun and "descendent" is the adjective

activerecord/CHANGELOG

@@ -5248,7 +5248,7 @@ in effect.  Added :readonly finder constraint.  Calling an association collectio
     end
   
   This will assume that settings is a text column and will now YAMLize any object put in that attribute. You can also specify
-  an optional :class_name option that'll raise an exception if a serialized object is retrieved as a descendent of a class not in
+  an optional :class_name option that'll raise an exception if a serialized object is retrieved as a descendant of a class not in
   the hierarchy. Example:
   
     class User < ActiveRecord::Base
@@ -5744,7 +5744,7 @@ _Misc_
 *0.8.2*
 
 * Added inheritable callback queues that can ensure that certain callback methods or inline fragments are
-  run throughout the entire inheritance hierarchy. Regardless of whether a descendent overwrites the callback
+  run throughout the entire inheritance hierarchy. Regardless of whether a descendant overwrites the callback
   method:
   
     class Topic < ActiveRecord::Base

activerecord/lib/active_record/base.rb

@@ -327,7 +327,7 @@ module ActiveRecord #:nodoc:
   #   User.find(user.id).preferences # => { "background" => "black", "display" => large }
   #
   # You can also specify a class option as the second parameter that'll raise an exception if a serialized object is retrieved as a
-  # descendent of a class not in the hierarchy. Example:
+  # descendant of a class not in the hierarchy. Example:
   #
   #   class User < ActiveRecord::Base
   #     serialize :preferences, Hash
@@ -2167,7 +2167,7 @@ module ActiveRecord #:nodoc:
           scoped_methods.last
         end
 
-        # Returns the class type of the record using the current module as a prefix. So descendents of
+        # Returns the class type of the record using the current module as a prefix. So descendants of
         # MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
         def compute_type(type_name)
           modularized_name = type_name_with_module(type_name)
@@ -2880,7 +2880,7 @@ module ActiveRecord #:nodoc:
         id
       end
 
-      # Sets the attribute used for single table inheritance to this class name if this is not the ActiveRecord::Base descendent.
+      # Sets the attribute used for single table inheritance to this class name if this is not the ActiveRecord::Base descendant.
       # Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to do Reply.new without having to
       # set <tt>Reply[Reply.inheritance_column] = "Reply"</tt> yourself. No such attribute would be set for objects of the
       # Message class in that example.

activerecord/lib/active_record/callbacks.rb

@@ -77,7 +77,7 @@ module ActiveRecord
   #
   # In that case, <tt>Reply#destroy</tt> would only run +destroy_readers+ and _not_ +destroy_author+. So, use the callback macros when
   # you want to ensure that a certain callback is called for the entire hierarchy, and use the regular overwriteable methods
-  # when you want to leave it up to each descendent to decide whether they want to call +super+ and trigger the inherited callbacks.
+  # when you want to leave it up to each descendant to decide whether they want to call +super+ and trigger the inherited callbacks.
   #
   # *IMPORTANT:* In order for inheritance to work for the callback queues, you must specify the callbacks before specifying the
   # associations. Otherwise, you might trigger the loading of a child before the parent has registered the callbacks and they won't

activerecord/lib/active_record/named_scope.rb

@@ -39,7 +39,7 @@ module ActiveRecord
       # Nested finds and calculations also work with these compositions: <tt>Shirt.red.dry_clean_only.count</tt> returns the number of garments
       # for which these criteria obtain. Similarly with <tt>Shirt.red.dry_clean_only.average(:thread_count)</tt>.
       #
-      # All \scopes are available as class methods on the ActiveRecord::Base descendent upon which the \scopes were defined. But they are also available to
+      # All \scopes are available as class methods on the ActiveRecord::Base descendant upon which the \scopes were defined. But they are also available to
       # <tt>has_many</tt> associations. If,
       #
       #   class Person < ActiveRecord::Base