Old mate in Paris welcomes rare beef (8)
I believe the answer is:
pastrami
'beef' is the definition.
(pastrami is a kind of beef)
'old mate in paris welcomes rare' is the wordplay.
'old' becomes 'past' (similar in meaning).
'mate in paris' becomes 'ami' ('friend' in French).
'welcomes' means one lot of letters goes inside another (in sense of 'invites in').
'rare' becomes 'r' (listed by Oxford Dictionary of Abbreviations).
'past'+'ami'='pastami'
'pastami' going around 'r' is 'PASTRAMI'.
(Other definitions for pastrami that I've seen before include "Highly seasoned cut of smoked beef" , "Seasoned smoked beef, served in thin slices" , "Tapered tuck; missile" , "Spicy smoked beef" , "Smoked, highly-seasoned cut of beef" .)