The Collaborative International Dictionary of English v.0.48:

Sup \Sup\, v. i. [See Supper.]
   To eat the evening meal; to take supper.
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         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.]
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         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.
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         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.
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         Tom Thumb had got a little sup.          --Drayton.
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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