shtup
Concise Oxford English Dictionary © 2008 Oxford University Press:
shtup /ʃtʊp/ (also schtup) vulgar slang
▶verb (shtups, shtupping, shtupped) have sex with. ▶noun an act of sexual intercourse.
– origin 1960s: Yiddish.
'shtup' also found in these Oxford entries:

