Multimethods are ambient actions. You could implement them with functions and any sort of type system. Maybe also a way to have variable-length parameter lists. If that's OO then functional programming is object-oriented programming.

Yes, functional programming is very similar to OO.

OO:

    class SomeType { 
        <data> ; 
        SomeOtherType function1() { 
            this.whatever ; 
            ... 
        }
    }

FP:

    data SomeType ...
    f1 :: SomeType -> SomeOtherType
    f1 this = whatever this >> ...

Same idea, different syntax. (Type classes will allow polymorphism, if that's what you're after.)

You are thinking of the abstraction in terms of its implementation. There is no reason why a method in a class would physically be in that class; the class just acts as a namespace:

   class Foo { method }
   Foo.method();

and

   (defmethod Foo.method ...)
   (Foo.method)

are the same.

Multimethods means that a method is dispatched not only on basis of the receveiving object (or read: first argument) but on basis of all arguments. The term is inherently related to OOP: http://en.wikipedia.org/wiki/Multimethod

You put it much better than I did; facts without rhetoric :-)