Only spirit mentioned? (4)
I believe the answer is:
sole
'only' is the definition.
(I know that only can be written as sole)
'spirit mentioned?' is the wordplay.
'spirit' becomes 'soul' (soul is a kind of spirit).
'mentioned?' shows a homophone (sound like) (I've seen 'mentioned' mean this).
'soul' sounds like 'SOLE'.
(Other definitions for sole that I've seen before include "European flatfish" , "Lone; part of foot" , "A lone sort of fish - lose it" , "A lone flat fish?" , "Dover - -" .)