Sheer endless choice (4)
I believe the answer is:
plum
'choice' is the definition.
(I've seen this before)
'sheer endless' is the wordplay.
'sheer' becomes 'plumb' (both can mean vertical).
'endless' means to remove the last letter.
'plumb' with its last letter removed is 'PLUM'.
(Other definitions for plum that I've seen before include "Brilliant" , "Fruit; something choice" , "Best; fruit" , "Lump of fruit" , "Dark purple" .)