Definitions for go under
sink, settle, go down, go under(verb)
go under, "The raft sank and its occupants drowned"
set, go down, go under(verb)
disappear beyond the horizon
"the sun sets early these days"
go by, go under(verb)
be called; go by a certain name
"She goes by her maiden name again"
Kernerman English Learner's Dictionary
(of a business) to fail
The company went under two years later.
to descend into a body of water
to be named, to call oneself
to go bankrupt, to collapse