Golf club missing head, say (5)
I believe the answer is:
utter
'say' is the definition.
(to utter something is to speak or say it)
'golf club missing head' is the wordplay.
'golf club' becomes 'putter' (I've seen this before).
'missing head' means to remove the first letter.
'putter' with its first letter removed is 'UTTER'.
(Other definitions for utter that I've seen before include "Give tongue to" , "Speak in absolute way" , "Absolutely" , "mouth" , "Without a single qualification" .)