Dog, male, possibly longer (7)
I believe the answer is:
mongrel
'dog' is the definition.
(mongrel is a kind of dog)
'male possibly longer' is the wordplay.
'male' becomes 'm' (common abbreviation).
'possibly' indicates an anagram.
'longer' with letters rearranged gives 'ongrel'.
'm'+'ongrel'='MONGREL'
(Other definitions for mongrel that I've seen before include "Cross-breed dog" , "unlike well-bred setter, say" , "Hybrid" , "of unknown variety" , "Cur" .)