descend vs go under

descend and go under both are verbs.

Word	Noun	Adjective	Verb	Adverb
descend	No	No	Yes	No
go under	No	No	Yes	No

As verbs, go under is a hyponym of descend; that is, go under is a word with a more specific, narrower meaning than descend:

descend (verb)	go under (verb)
come as if by falling	be called; go by a certain name
move downward and lower, but not necessarily all the way	go under
do something that one considers to be below one's dignity	disappear beyond the horizon
come from; be connected by a relationship of blood, for example