Hairstyle for every mother's head (4)
I believe the answer is:
perm
'hairstyle' is the definition.
(perm is a kind of hairstyle)
'every mother's head' is the wordplay.
'every' becomes 'per' (I've seen this in other clues).
'head' says to take the initial letters.
The first letter of 'mothers' is 'm'.
'per'+'m'='PERM'
'for' is the link.
(Other definitions for perm that I've seen before include "Wavy hairstyle" , "Hairdo - combination on football pools" , "Give a wave" , "Old-fashioned haircut" , "To curl (hair)" .)