Where you may use a gun scope (5)
I believe the answer is:
range
'scope' is the definition.
(synonyms)
'where you may use a gun' is the wordplay.
I cannot really understand how this works, but
'a' could be 'an' and 'an' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for range that I've seen before include "Scope, extent" , "Open land for livestock in the US" , "Large, grassy land for livestock in the US" , "Cut; cultivated plant" , "practise shooting here" .)