sub 2 
(sŭb) Informal
(sŭb) Informal n.
A substitute.
v. subbed, sub·bing, subs
v.intr.
To act as a substitute: a graduate student subbing for the professor.
v.tr.
1. To put or use (a person or thing) as a substitute: The coach subbed fresh players toward the end of the game. The cook subbed oil for butter.
2. Usage Problem To replace; substitute: The player was subbed after she committed two errors. Sub the chicken with tofu to make the dish vegetarian. See Usage Note at substitute.