The Collaborative International Dictionary of English v.0.48:

Gerund \Ger"und\, n. [L. gerundium, fr. gerere to bear, carry,
   perform. See Gest a deed, Jest.] (Lat. Gram.)
   [1913 Webster]
   1. A kind of verbal noun, having only the four oblique cases
      of the singular number, and governing cases like a
      participle.
      [1913 Webster]

   2. In Modern English, the -ing form of a verb, when
      functioning as a noun; as, running is good for the heart.
      [PJC]

   3. (AS. Gram.) A verbal noun ending in -e, preceded by to and
      usually denoting purpose or end; -- called also the
      dative infinitive; as, "Ic h[ae]bbe mete t[^o] etanne"
      (I have meat to eat.).
      [1913 Webster]

WordNet (r) 3.0 (2006):

gerund
    n 1: a noun formed from a verb (such as the `-ing' form of an
         English verb when used as a noun)