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.
"a perfectly cromulent word"

"he has just embiggened the office of town crier with that cromulent speech"
by RathminesPimp October 26, 2004
Over use of spray paint. Particularly many different colours seen together.
The graffiti was a cromulent and nauseating disgrace.
by Brett Burton April 23, 2003
Used in an ironical sense to mean legitimate, and therefore, in reality, spurious and not at all legitimate. Assumes common knowledge of the inherent Simpsons reference.
Yes Professor Smith, these citations are perfectly cromulent. chuckle
I believe this term originated in the Animated Television Series "The Simpsons"
Edna: Embiggens? I never heard that word before I moved to Springfield.

Ms.Hoover: I don't know why. It's a perfectly cromulent word.
by jimjam June 8, 2004
Expression used to legitimize another expression of dubious existence. Used in the ironic sense in that it defends the questionable use of an illigitimate or slang word with another made-up expression. The intent of the phrase is generally used in conjunction with insults to high talkers, english majors and otherwise insufferable people who feel the need to correct others. Often accompanied by a punch to the stomach.
You grok what I mean, yo? (person in the know) There is no such word as grok! (Buzz kill) Grok is an exceptionally cromulent word. (street wise hommes)
by Anonymous July 22, 2003
The state or act of being cromulent.
The third commandment of the Georgia Guidestones put in place by the Rosicrucian Order suggests that as long as the words one chooses to use cromulate well, it is irrelevant what the Oxford English Dictionary has to say on the matter.
by ManyNamesNoneTrue April 17, 2020