The Collaborative International Dictionary of English v.0.48:

Undermeal \Un"der*meal`\, n. [AS. under under + m?l part or
   portion; cf. AS. underm?l midday. See Under, Meal a part,
   and cf. Undern.]
   1. The inferior, or after, part of the day; the afternoon.
      [Obs. or Prov. Eng.]
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            In undermeals and in mornings.        --Chaucer.
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   2. Hence, something occurring or done in the afternoon; esp.,
      an afternoon meal; supper; also, an afternoon nap; a
      siesta. [Obs. or Prov. Eng.]
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            Another great supper, or undermeal, was made ready
            for them, coming home from ditching and plowing.
                                                  --Withals
                                                  (1608).
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            I think I am furnished with Cattern [Catharine]
            pears for one undermeal.              --B. Jonson.
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            In a narrower limit than the forty years' undermeal
            of the seven sleepers.                --Nash.
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