Old sheep one for meat (8)
I believe the answer is:
pastrami
'for meat' is the definition.
(pastrami is a kind of meat)
'old sheep one' is the wordplay.
'old' becomes 'past' (similar in meaning).
'sheep' becomes 'ram' (male sheep).
'one' becomes 'I' (Roman numeral).
'past'+'ram'+'i'='PASTRAMI'
(Other definitions for pastrami that I've seen before include "Highly seasoned cut of smoked beef" , "Spiced sliced beef" , "Spicy smoked beef" , "Sliced cured beef" , "Tapered tuck; missile" .)