Interchangeable
Part of speech: adjective
Definition: Freely substitutable. May be swapped at will.
Example sentence: Any good software engineer will tell you that a compiler and an interpreter are interchangeable.
Similar
Part of speech: adjective
Definition: Having traits or characteristics in common; alike, comparable.of triangles, etc., having corresponding angles equal and corresponding line segments proportional (the same shape, but possibly different size).
Example sentence: Poetry and lyrics are very similar. Making words bounce off a page.