The largest living bird (7)
I believe the answer is:
ostrich
'the largest living bird' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ostrich that I've seen before include "Runner" , "The head-in-the-sand bird" , "Bird burying its head in the sand" , "with a big nest egg" , "Torch is raised for big bird" .)