Beep (4)
I believe the answer is:
honk
'beep' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for honk that I've seen before include "Cry of a goose - sound of a horn" , "Toot one's horn" , "Cry of the wild goose" , "Toot of a horn - cry of a goose - smell nasty" .)