Source : WordNet®

boil down
     v 1: be the essential element; "The proposal boils down to a
          compromise" [syn: {reduce}, {come down}]
     2: be cooked until very little liquid is left; "The sauce
        should reduce to one cup" [syn: {reduce}, {decoct}, {concentrate}]
     3: cook until very little liquid is left; "The cook reduced the
        sauce by boiling it for a long time" [syn: {reduce}, {concentrate}]