The cold one, indeed, foolishly caught will clinch it (6)
I believe the answer is:
decide
'indeed foolishly caught will clinch it' is the definition.
I can't tell whether this defines the answer.
'the cold one' is the wordplay.
I cannot really understand how this works, but
'cold' could be 'c' (eg on taps) and 'c' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for decide that I've seen before include "Reach a conclusion" , "Resolve or give a judgment" , "Reach a judgment" , "Resolve; give judgement" , "Resolve, settle (issue)" .)