Is unsuccessful (5)
'is unsuccessful' is the definition.
(to lose is to be unsuccessful)
This is the entire clue.
(Other definitions for loses that I've seen before include "Goes down" , "Fails to win" , "Is unable to find" , "Mislays or is defeated" , "Misplaces" .)
'is unsuccessful' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for fails that I've seen before include "Doesn't pass" , "Does not succeed" , "Is unsuccessful" .)