Male just lacking initial strength (5)
I believe the answer is:
might
'strength' is the definition.
(I know that might is a type of strength)
'male just lacking initial' is the wordplay.
'male' becomes 'm' (common abbreviation).
'just' becomes 'right' (similar in meaning).
'lacking initial' means to remove the first letter.
'right' with its first letter taken away is 'ight'.
'm'+'ight'='MIGHT'
(Other definitions for might that I've seen before include "Strength - could possibly" , "May, in the past" , "Great power/strength" , "Great power, strength" , "It expresses possibility" .)