The word has several idiomatic and slang uses.

It can be used to say that something includes, consists of, is composed of something. Normally this would be yugh.

It can be used to say that someone is absorbed in something, as in Jim 'uch QoQDaj Jim is absorbed by his music (literally His music holds Jim).

Sentences that use this word:

naQ megh'an 'er'In ghap yI'uch. naQ 'er'In megh'an ghap yI'uch.
Grasp either end of the stick ("grasp the end or the other end of the stick") (HQ 12.2)

naQ megh'an yI'uchHa'. naQ 'er'In yI'uchHa'.
Let go of the end of the stick. (HQ 12.2)

Cen be used to mean "lock" in the sense of locking on a target with a weapons system or transporter beam:

DoS 'uchta'
he/she locked on the target

ghoptelDaj yI'uch
Lock onto his signal!

'uch can be used to tell someone to keep the change when dealing with money. "Change" in this sense is chuv "leftover." "Keep the change," said to a merchant, for example, would be chuvmey tI'uch (or, if it made sense, chuv yI'uch), literally "hold (on to) the leftover(s)!" (This could be ambiguous in a restaurant, of course, so one should be certain that context makes clear what is meant by chuv.)