The verb qu' literally means "be fierce." In its slang sense, it may be used adjectivally, as in taj qu' ("excellent knife"; literally, "fierce knife"), or as the main verb in a sentence, as in qu' taj ("the knife is excellent"; literally, "the knife is fierce"). Though, from the Klingon point of view, equating being "fierce" with being "great, wonderful," and so on seems quite natural, the slang meaning of qu' probably receives further support because it sounds just like the verb suffix -qu', which is used for emphasis (compare Qatlh, "difficult," and Qatlhqu', "very difficult"). When applied to people or animals, it is not always clear whether the slang or nonslang meaning of qu' is intended. That is, SuvwI' qu' ("fierce warrior") could be interpreted literally, or it could mean "excellent warrior."

When applied to anything other than people or animals, the slang meaning is more likely. Thus, may' qu' ("fierce battle") is really a way of saying "excellent battle." In Klingon, only a participant in a battle, not the battle itself, can literally be described as "fierce." The word qu' may also be used as an exclamation ("Great!" "Wonderful!"). In this sense, it seems to be interchangeable with chong (literally, "be vertical").

The slang usage of qu' is currently extremely common among Klingons, and it has pretty much displaced another slang term with the same set of meanings ("excellent, wonderful, etc."), Huv (literally, "be clear, not obstructed"), which was in vogue not all that long ago. The use of Huv for "excellent" is now considered old-fashioned. This is also the case with nong ("passionate"), an even older slang term for "excellent." (As of this writing, the slang usage of nong seems to be making a comeback, but it is still too early to say whether this will really happen.) Nonslang verbs expressing similar ideas are Dun ("be wonderful, great"), pov ("be excellent"), and, as an exclamation, maj! ("Good!").

(KGT 164f.) To describe someone as SaS is certainly insulting, as in SaS DIvI' HoD ("The Federation captain is shallow"--that is, literally, "The Federation captain is horizontal"). ... A slang word with a meaning similar to SaS is natlh (literally, "consume, use up" [see page 155]). The opposite meaning--that is, profound, thorough and good--is often expressed by the slang verbs chong (literally, be vertical) and qu' (literally, be fierce).

(KGT 149): See also qu' (literally, be fierce), another slang term used to express approval.

(KGT 155): "Slang terms expressing the opposite of natlh--that is, approval--are chong (literally, be vertical) and qu' (literally, be fierce).

Add to these the new slang verb vIl "be cool" (as in chic) from qep'a' 2018.