Thin candle (5)
I believe the answer is:
'thin candle' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for taper that I've seen before include "Gradually become thinner" , "Spill - become narrower towards one end" , "Convex shape that narrows toward a point" , "Tail off; a spill" , "Fall off" .)