Sub spread (4)
I believe the answer is:
mayo
'sub spread' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mayo that I've seen before include "County of north-west Ireland" , "Salad dressing (abbr)" , "Saucy thing" , "Irish county (county town, Castlebar)" , "Thick creamy dressing" .)