Learnt to play horn? (6)
I believe the answer is:
antler
'horn?' is the definition.
(I know that antler is a type of horn)
'learnt to play' is the wordplay.
'to play' indicates an anagram.
'learnt' is an anagram of 'ANTLER'.
(Other definitions for antler that I've seen before include "Stag horn" , "Bony outgrowth in the deer family" , "part of Rudolph" , "Animal's extension" , "Stag's horn" .)