The opposite of overused.
A word that you had in your daily vocabulary but somehow forgot. It might even got overused but because you haven't used it in a long time it got underused again
Guy1: There's a wet t-shirt contest in the hotel.
Guy1: They're still looking for 3 judges btw.
Guy3: We gotta register as judges.
Guy1: Already done guys, and guess what we were already picked
Guy1: Guys that's not legendary, that's fucking ZEDERN!
Guy2: God totally forgot zedern, totally underused :P