Dogs in underwear (6)
I believe the answer is:
boxers
This clue is a double definition.
'dogs' is the first definition.
(boxer is a kind of dog)
'underwear' is the second definition.
(I know that boxers is a underwear)
'in' acts as a link.
(Other definitions for boxers that I've seen before include "Dogs or men's loose underpants" , "Craters" , "Dogs or pugilists" , "Men's shorts for pugilists" , "Pugs; dogs" .)