A threesome firmly quashed -- loser, big time! (7)

I think it could be either:

Which length description are you looking for?:

7,2,3,4

slimmer

If this is the answer, I'm afraid I cannot explain it.

(Other definitions for slimmer that I've seen before include "thinner" , "with less fat" , "More slenderly built" , "One attempting to lose weight" , "in better shape?" .)

I've seen this clue in The Guardian.

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