Only to lose out! (4)
I believe the answer is:
sole
'only' is the definition.
(I know that only can be written as sole)
'lose out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'lose' with letters rearranged gives 'SOLE'.
'to' acts as a link.
(Other definitions for sole that I've seen before include "Exclusive class of fish" , "A lonely sort of flatfish" , "Fish; part of foot" , "Kind of fish - lose it" , "Shoe part -- lone" .)