Not simply used to refer to a frequently used word as per the use in "a perfectly cromulent word" but may be better defined as germane, or apt, synonomous with appropriate, or fitting.
This defintion suits both uses in The Simpsons' famous episode.
Synonyms for cromulant
On this page, you will find 30 slang terms related to cromulant. Some of the top words include: anywho, Mmm!, computar, fedda, that's crip, and 25 more.