Ermine, in the summer
I believe the answer is:
stoat
'ermine in the summer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stoat that I've seen before include "Source of ermine" , "Weasel, ermine" , "Ermine in summertime?" , "Member of the weasel family" , "Small carnivorous mammal of the weasel family" .)