Hi,

Yes, a +define_method+ method is an instance method of the +Module+ class,
as you said. However, the method is PRIVATE [1], so you can't find it by using
your code.
Please use following code instead.

(on ruby 1.9.2-p180)
Mocdule.private_instance_methods.include? :define_method
=> true

[1] http://ruby-doc.org/core/classes/Module.html#M000497

Regards,
-- 
NOBUOKA Yu