This is an old analysis, and before I really got into the etymology analysis, but still useful.
It's amazing the difference an "a" versus an "e" can make, including the fact that this word with the "e" (Mordent) is frequently mispelled as "mordant" which caused me all manner of confusion. Mordent being a type of musical ornamentation with which I am familiar (although it is not my style of singing - baroque) and mordant being a type of wit. And the subtlety of pronounciation could be distracting. Of course, if they were being pronounced correctly, mordent would be done with that French nasal sound that I keep griping about and an accent on the second syllable, but it is so frequently mispronounced with the accent on the first syllable in that horrible American twang that hammers on the "n", obscuring the vowel entirely and making it sound like mordent.
His mordant wit and plebian humor served him well ingratiating himself to his fellow inmates, although his use of those words often got him beat up for being too pretentious. And every time I hear "mordant" (or even "mordent") I still hear a "death" root, not a "biting" root. And plebian reminds me of the whole fraternity system with the indoctrination period as "plebes", not better than slaves to the vested brothers. Again, if I were to use such a term as plebian, I would choose the French over the Latin: declassé, or go with base, which I find is another underutilized word, particularly as it is such a good adjective. Or if you really want to get descriptive, trailer trash (or just trash) has such a nice connotative ring to it.