Son needs head covering in strong draught (4)
I believe the answer is:
swig
'strong draught' is the definition.
(as in a swig of alcohol)
'son needs head covering' is the wordplay.
'son' becomes 's'.
'needs' is a charade indicator (letters next to each other).
'head covering' becomes 'wig'.
's'+'wig'='SWIG'
'in' acts as a link.
(Other definitions for swig that I've seen before include "Large swallow" , "(Take) quick drink from bottle" , "Large gulp from the bottle" , "Drink (a deep draught)" , "Large draught of drink" .)