The Collaborative International Dictionary of English v.0.48:

Lunch \Lunch\, v. i. [imp. & p. p. Lunched; p. pr. & vb. n.
   Lunching.]
   To take luncheon. --Smart.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lunch \Lunch\ (l[u^]nch), n. [Of uncertain etymol. Cf. Prov.
   Eng. nunc a lump.]
   A luncheon; specifically, a light repast between breakfast
   and dinner, most commonly about noontime.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

lunch
    n 1: a midday meal [syn: lunch, luncheon, tiffin,
         dejeuner]
    v 1: take the midday meal; "At what time are you lunching?"
    2: provide a midday meal for; "She lunched us well"

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "lunch":
   TV dinner, alfresco meal, barbecue, board, break bread with,
   breakfast, brunch, buffet supper, clambake, coffee break, cook out,
   cookout, dine, dine out, diner, dinner, eat out, elevenses,
   fish fry, high tea, hot luncheon, luncheon, mash, meat breakfast,
   mess with, petit dejeuner, picnic, sup, supper, tea, tea break,
   teatime, tiffin, wiener roast, wienie roast