Sort out a profit -- one grand, possibly (10)
'grand possibly' is the definition.
(grand is a kind of pianoforte)
'sort out a profit one' is the wordplay.
'sort out' indicates anagramming the letters.
'aprofitone' is an anagram of 'PIANOFORTE'.
(Other definitions for pianoforte that I've seen before include "Joanna", "Keyboard instrument", "might be grand".)