Supplement that beekeeper must take to get horn (3,3)
I believe the answer is:
eke out
'supplement' is the definition.
(eking out is a kind of supplementing)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for eke out that I've seen before include "Just about manage to make a living" , "Make living laboriously" , "Make (meagre supplies) last" , "Make a meagre living" , "Make last, use sparingly" .)