Plastic cup brand (4)
I believe the answer is:
solo
'plastic cup brand' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for solo that I've seen before include "something for one to do" , "Unaccompanied passage" , "On one's own, unaccompanied" , "Han - (Star Wars); fly unaccompanied" , "(Piece performed) on one's own" .)