Mayonnaise ingredient (3)
I believe the answer is:
egg
'mayonnaise ingredient' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for egg that I've seen before include "nit? Just a bit!" , "It comes before or after the chicken?" , "Incite; ovum" , "Urge (someone on )" , "Reproductive unit" .)