Bluff chap's first kid (4)
I believe the answer is:
crag
'bluff' is the definition.
(thesaurus)
'chap's first kid' is the wordplay.
'first' says to take the initial letters.
'kid' becomes 'rag' (I've seen this in other clues**).
The initial letter of 'chap' is 'c'.
'c'+'rag'='CRAG'
(Other definitions for crag that I've seen before include "Steep rocky cliff" , "Avant-garde" , "Steep or rugged cliff face" , "Steep rugged rock or cliff" , "Steep, rugged peak" .)