Labour in grief for Tony (6)
I believe the answer is:
effort
'labour' is the definition.
(effort is a kind of labour)
'in grief for tony' is the wordplay.
'in' indicates a hidden word.
'EFFORT' can be found hidden inside 'grief for tony'.
(Other definitions for effort that I've seen before include "The use of physical or mental energy" , "Serious industry - attempt" , "For eft (anag.)" , "Try - labour - pains" , "Hard mental or physical work" .)