Possibly cools engines (5)
I believe the answer is:
locos
'engines' is the definition.
Both the definition and answer are plural nouns.
Maybe you can see an association between them that I don't see?
'possibly cools' is the wordplay.
'possibly' is an anagram indicator.
'cools' anagrammed gives 'LOCOS'.
Can you help me to learn more?
(Other definitions for locos that I've seen before include "Railway engines" , "trains" .)