Monkey working in a tram (7)
I believe the answer is:
tamarin
'monkey' is the definition.
(tamarin is a kind of monkey)
'working in a tram' is the wordplay.
'working' is an anagram indicator.
'in'+'a'+'tram'='inatram'
'inatram' anagrammed gives 'TAMARIN'.
(Other definitions for tamarin that I've seen before include "Main art (anag) - monkey" , "Small monkey of the marmoset family" .)