Drink trademark, ultimately legendary (6)
I believe the answer is:
brandy
'drink' is the definition.
(brandy is a kind of drink)
'trademark ultimately legendary' is the wordplay.
'trademark' becomes 'brand' (I've seen this before).
'ultimately' suggests the final letters.
The final letter of 'legendary' is 'y'.
'brand'+'y'='BRANDY'
(Other definitions for brandy that I've seen before include "Strong liquor" , "Eau de vie" , "Cognac, calvados, armagnac etc" , "See 1" , "Samuel Johnson's drink fit for heroes" .)