Some said that's a relief (4)
I believe the answer is:
phew
'that's a relief' is the definition.
(phew is an expression of relief)
'some said' is the wordplay.
'some' becomes 'few' (associated in meaning).
'said' shows a homophone (sound like).
'few' sounds like 'PHEW'.
(Other definitions for phew that I've seen before include "Expression of relief" , "Sound relieved" , "Gosh, that's a relief!" , "Gosh, I'm sweltering!" , "thank goodness!" .)