The Collaborative International Dictionary of English v.0.48:

Sup \Sup\, v. i. [See Supper.]
   To eat the evening meal; to take supper.
   [1913 Webster]

         I do entreat that we may sup together.   --Shak.
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The Collaborative International Dictionary of English v.0.48:

Sup \Sup\, v. t.
   To treat with supper. [Obs.]
   [1913 Webster]

         Sup them well and look unto them all.    --Shak.
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The Collaborative International Dictionary of English v.0.48:

Sup \Sup\ (s[u^]p), v. t. [imp. & p. p. Supped; p. pr. & vb.
   n. Supping.] [OE. soupen to drink, AS. s[=u]pan; akin to D.
   zuipen, G. saufen, OHG. s[=u]fan, Icel. s[=u]pa, Sw. supa,
   Dan. s["o]be. Cf. Sip, Sop, Soup, Supper.]
   To take into the mouth with the lips, as a liquid; to take or
   drink by a little at a time; to sip.
   [1913 Webster]

         There I'll sup
         Balm and nectar in my cup.               --Crashaw.
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The Collaborative International Dictionary of English v.0.48:

Sup \Sup\, n.
   A small mouthful, as of liquor or broth; a little taken with
   the lips; a sip.
   [1913 Webster]

         Tom Thumb had got a little sup.          --Drayton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sup
    n 1: a small amount of liquid food; "a sup of ale" [syn:
         swallow, sup]
    v 1: take solid or liquid food into the mouth a little at a time
         either by drinking or by eating with a spoon

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "sup":
   beverage, bib, bite, board, booze, break bread with, breakfast,
   bumper, cast, cook out, dash, dine, dine out, dinner, draft,
   drain the cup, dram, drench, drink, drink bottoms-up, drink deep,
   drink hard, drink in, drink off, drink to, drink up, drop, eat out,
   follow strong drink, gargle, gleam, grog, gulp, guzzle, hint, idea,
   imbibe, intimation, jigger, jolt, knock back, lap, lap up,
   libation, lick, look, lunch, mess with, nip, peg, picnic, pledge,
   portion, potation, potion, pull, quaff, round, round of drinks,
   sample, savor, scintilla, shade, shadow, shot, sip, slurp, smack,
   smattering, smell, snifter, snort, soak, soupcon, spark, spot,
   sprinkling, suck, suck in, suckle, suggestion, suspicion, swallow,
   swig, swill, taste, taste of, thought, tincture, tinge, tipple,
   toast, tope, toss, toss down, toss off, tot, touch, trace,
   wash down, wet