1. Position in opposition or contrast to, either physically or conceptually
   "The white walls were set against dark furniture"; "Her optimism was set against his pessimism"
    
2. Cause to be hostile or opposed to
   "The incident set the two groups against each other"
    
3. Deduct or subtract from a total
   "The expenses were set against the profits"

Derived forms: setting against, sets against, set against