Glen makes lead fly (4)
I believe the answer is:
dale
'glen' is the definition.
(I've seen this in another clue)
'lead fly' is the wordplay.
'fly' indicates anagramming the letters.
'lead' is an anagram of 'DALE'.
'makes' acts as a link.
(Other definitions for dale that I've seen before include "See 8" , "Valley, as in Yorkshire" , "Valley; old radio soap family" , "Up hill and down . . . ." , "depression" .)