Explore a glen, coming across one of its residents? (5)
I believe the answer is:
eagle
'one of its residents?' is the definition.
I can't tell whether this defines the answer.
'explore a glen coming across' is the wordplay.
'across' says the answer is hidden in the clue.
'EAGLE' is hidden within 'explore a glen coming'.
(Other definitions for eagle that I've seen before include "Keen-eyed bird" , "flier" , "high-flier" , "Aglee (anag.)" , "High-flyer" .)