The Collaborative International Dictionary of English v.0.48:

Runt \Runt\, n. [Written also rant.] [Scot. runt an old cow,
   an old, withered woman, a hardened stem or stalk, the trunk
   of a tree; cf. D. rund a bullock, an ox or cow, G. rind. Cf.
   Rother, a.]
   1. (Zool.) Any animal which is unusually small, as compared
      with others of its kind; -- applied particularly to
      domestic animals.
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   2. (Zool.) A variety of domestic pigeon, related to the barb
      and carrier.
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   3. A dwarf; also, a mean, despicable, boorish person; -- used
      opprobriously.
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            Before I buy a bargain of such runts,
            I'll buy a college for bears, and live among 'em.
                                                  --Beau. & Fl.
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   4. The dead stump of a tree; also, the stem of a plant. [Obs.
      or Prov. Eng.] --Halliwell.
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            Neither young poles nor old runts are durable.
                                                  --Holland.
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WordNet (r) 3.0 (2006):

runt
    n 1: disparaging terms for small people [syn: runt, shrimp,
         peewee, half-pint]