Twist key tip (4)
I believe the answer is:
bend
'twist' is the definition.
(synonyms)
'key tip' is the wordplay.
'key' becomes 'b' (eg B major, musical key).
'tip' becomes 'end' (tip can mean the end of something).
'b'+'end'='BEND'
(Other definitions for bend that I've seen before include "Influence, bow" , "Arc" , "Turn, flex" , "Turn - buckle" , "Form a curve" .)