1. Working as a substitute for someone who is ill or on leave of absence
   "She made extra money by subbing for teachers on maternity leave";
   - substituting

1. Put in the place of another; switch seemingly equivalent items
   "She subbed margarine for butter in the recipe";
   - substitute, replace, interchange, exchange
    
2. Be a substitute
   "The young teacher had to sub for the sick colleague";
   - substitute, stand in, fill in
    
3. Act or speak as a replacement (for someone or something)
   "He often subs for absent teachers";
   - substitute, deputize, deputise [Brit], step in

Derived forms: subbings

Type of: alter, change, exchange, interchange, modify, replace, supercede [non-standard], supersede, supervene upon, supplant, work

Encyclopedia: Subbing