Arctic rodent (7)
I believe the answer is:
lemming
'arctic rodent' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lemming that I've seen before include "Northern rodent" , "Rodent to describe someone who rushes headlong to destruction" , "Rodent that follows others headlong over a cliff" , "One misjudges landing" , "Arctic rodent; one going blind to disaster" .)