WordWeb Online

1. Be the essential element
   "The proposal boils down to a compromise"
   - reduce, come down
    
2. Be cooked until very little liquid is left
   "The sauce should boil down to one cup"
   - reduce, decoct [archaic], concentrate
    
3. Cook until very little liquid is left
   "The cook boiled down the sauce by boiling it for a long time"
   - reduce, concentrate

Derived forms: boiling down, boils down, boiled down

Type of: become, decrease, diminish, fall, lessen, minify, turn