Medium drink for bloke (4)
I believe the answer is:
male
'for bloke' is the definition.
(bloke means a man)
'medium drink' is the wordplay.
'medium' becomes 'm' (as in UK clothing sizes).
'drink' becomes 'ale' (type of beer).
'm'+'ale'='MALE'
(Other definitions for male that I've seen before include "Maldives capital; masculine" , "A gender" , "Lame sort of fellow" , "man?" , "One cannot have babies" .)