Keen — for one shot to the top (5)
I believe the answer is:
dirge
'keen' is the definition.
(I've seen this before)
'for one shot to the top' is the wordplay.
'for one' becomes 'eg' (both can mean 'for example').
'shot' becomes 'rid'.
'to the top' says the letters should be written backwards (in a down clue, letters are written bottom to top).
'eg'+'rid'='egrid'
'egrid' backwards is 'DIRGE'.
(Other definitions for dirge that I've seen before include "Threnody" , "Funereal hymn" , "Funereal music" , "Funeral lament" , "dreary tune" .)