Direct pleasure offered by King’s mistress mostly (6)
I believe the answer is:
funnel
'direct' is the definition.
(as in guiding through a funnel)
'pleasure offered by king's mistress mostly' is the wordplay.
'pleasure' becomes 'fun' (I've seen this in other clues).
'offered by' means one lot of letters go next to another.
'king's mistress' becomes 'nell' (mistress of Charles II).
'mostly' means to remove the last letter.
'nell' with its final letter taken off is 'nel'.
'fun'+'nel'='FUNNEL'
(Other definitions for funnel that I've seen before include "Chimney; pourer" , "Convey" , "Kind of tube for pouring wide at top and narrow at bottom" , "Pipe for pouring liquids into small openings" , "Conical utensil with narrow and wide ends" .)