Oil processed into fine condiment (5)
I believe the answer is:
aioli
'condiment' is the definition.
(aioli is a kind of condiment)
'oil processed into fine' is the wordplay.
'processed' indicates an anagram.
'into' means one lot of letters goes inside another.
'fine' becomes 'ai' (resembles A1, informal term for top quality).
'oil' with letters rearranged gives 'iol'.
'iol' placed inside 'ai' is 'AIOLI'.
(Other definitions for aioli that I've seen before include "mayonniase" , "Sort of mayonnaise" , "Mayonnaise with garlic" , "garlic dip" , "Garnish" .)