Long for a troop leader with vision (5)
I believe the answer is:
sight
'vision' is the definition.
(I know that vision can be written as sight)
'long for a troop leader' is the wordplay.
'long' becomes 'sigh' (both can mean to yearn).
'for' means one lot of letters go next to another.
'leader' indicates taking the first letters.
The first letter of 'troop' is 't'.
'sigh'+'t'='SIGHT'
'with' acts as a link.
(Other definitions for sight that I've seen before include "Notice" , "Vision, ability to see" , "Spectacle; aiming aid" , "something to behold" , "good deal" .)