Engineer in a car plant (6)
I believe the answer is:
arnica
'plant' is the definition.
(arnica is a kind of plant)
'engineer in a car' is the wordplay.
'engineer' indicates anagramming the letters.
'in'+'a'+'car'='inacar'
'inacar' is an anagram of 'ARNICA'.
(Other definitions for arnica that I've seen before include "Herb used for treating bruises" , "Application" , "Tincture of mountain tobacco, good for bruises, etc" , "Plant used to treat bruises" , "Bruise treatment" .)