The Collaborative International Dictionary of English v.0.48:

Quaff \Quaff\, v. t. [imp. & p. p. Quaffed; p. pr. & vb. n.
   Quaffing.] [For quach, fr. Gael. & Ir. cuach a drinking
   cup; cf. L. caucus a drinking vessel. Cf. Quaigh.]
   To drink with relish; to drink copiously of; to swallow in
   large draughts. "Quaffed off the muscadel." --Shak.
   [1913 Webster]

         They eat, they drink, and in communion sweet
         Quaff immortality and joy.               --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quaff \Quaff\, v. i.
   To drink largely or luxuriously.
   [1913 Webster]

         Twelve days the gods their solemn revels keep,
         And quaff with blameless Ethiops in the deep. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

quaff
    n 1: a hearty draft
    v 1: to swallow hurriedly or greedily or in one draught; "The
         men gulped down their beers" [syn: gulp, quaff, swig]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "quaff":
   beverage, bib, booze, bumper, draft, drain the cup, dram, drench,
   drink, drink bottoms-up, drink deep, drink hard, drink in,
   drink off, drink to, drink up, follow strong drink, gargle, grog,
   gulp, guzzle, imbibe, knock back, lap, lap up, libation, nip, peg,
   pledge, portion, potation, pull, sip, slurp, snort, soak, suck,
   suck in, suckle, sup, swallow, swig, swill, tipple, toast, tope,
   toss, toss down, toss off, tot, wash down