Male against small insect (6)
I believe the answer is:
mantis
'insect' is the definition.
(mantis is a kind of insect)
'male against small' is the wordplay.
'male' becomes 'm' (common abbreviation).
'against' becomes 'anti' (I've seen this before).
'small' becomes 's' (abbreviation - e.g. clothes size).
'm'+'anti'+'s'='MANTIS'
(Other definitions for mantis that I've seen before include "Insect often seen in praying posture" , "Carnivorous insect, which rests as if in prayer" , "may be praying" , "Praying insect at matins" , "Praying ..., long-bodied, large-eyed insect" .)