butter alternative (9)
(Other definitions for margarine that I've seen before include "Reg and Marian make a butter substitute" , "Is Ma angrier at this spread?" , "Vegetable fat" , "Substitute spread for butter" , "Fat-based butter substitute" .)
'butter alternative' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oleo that I've seen before include "Fatty substance" , "Marge" , "Prefix indicating oily" , "Oil used in making margarine" .)
(Other definitions for oil that I've seen before include "Thick liquid that doesn't dissolve in water" , "Type of fuel" , "Fluid lubricant" , "Fossil fuel" , "Lubricate; fuel" .)