{qIvon} is a bit of show-gibberish from DS9 that was retconned into a real word. Dax is trying to prove to Kor that she's Kor's old pal Curzon Dax, and she tells him "your left QiVon aches every time your ship hits warp eight." According to the Star Trek Encyclopedia (or, at least, according to what Memory Alpha says is according to the Star Trek Encyclopedia), this is supposed to be the Klingon word for "knee", which would just be {qIv}.

I wonder if there's some way to reconcile the two definitions -- the intended Star-Trek-writer's-room definition of "knee" and the Maltz definition of "unspecified body part". (We don't really need to reconcile them, I suppose, but it's always nice when the show canon and the language canon get along.) Perhaps it's a structure associated with the knee somehow that has no analogue in human anatomy. Etymologically, it looks like a contraction of {qIv von} "it entraps the knee" -- maybe it's some kind of tissue that surrounds the knee. Or perhaps it's just a dialect word for "knee", but Maltz was embarassed to talk about it because it's from a politically-disfavored dialect, or there's some crude pun associated with the term he didn't want to share.

I am, of course, speculating wildly.