Taunt rich setter, not well (4)
I believe the answer is:
jeer
'taunt' is the definition.
(jeering is a kind of taunting)
'rich setter not well' is the wordplay.
'rich setter' becomes 'jeweller' (to set can mean to mount a stone in jewellery).
'not' indicates named letters should be taken away.
'jeweller' with 'well' taken out is 'JEER'.
(Other definitions for jeer that I've seen before include "Scoff, deride, mock" , "Barrack" , "Tease" , "Mock - laugh at" , "Laugh at with derision" .)