tuber

from WordNet (r) 3.0 (2006)

tuber
    n 1: a fleshy underground stem or root serving for reproductive
         and food storage
    2: type genus of the Tuberaceae: fungi whose fruiting bodies are
       typically truffles [syn: {Tuber}, {genus Tuber}]

from The Collaborative International Dictionary of English v.0.48

Tuber \Tu"ber\, n.[L., a hump. knob; probably akin to tumere to
   swell. Cf. {Tumid}.]
   1. (Bot.)
      (a) A fleshy, rounded stem or root, usually containing
          starchy matter, as the potato or arrowroot; a
          thickened root-stock. See Illust. of {Tuberous}.
      (b) A genus of fungi. See {Truffle}.
          [1913 Webster]

   2. (Anat.) A tuberosity; a tubercle.
      [1913 Webster]