The Collaborative International Dictionary of English v.0.48:

Nab \Nab\, v. t. [imp. & p. p. Nabbed (n[a^]bd); p. pr. & vb.
   n. Nabbing.] [Dan nappe, or Sw. nappa.]
   1. To catch or seize suddenly or unexpectedly. [Colloq.]
      --Smollett.
      [1913 Webster]

   2. To capture; to arrest; as, the police nabbed the culprit
      wtrying to hide in the basement.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Nab \Nab\ (n[a^]b), n. [Cf. Knap, Knop, Knob.]
   1. The summit of an eminence. [Prov. Eng.] --Halliwell.
      [1913 Webster]

   2. (Firearms) The cock of a gunlock. --Knight.
      [1913 Webster]

   3. (Locksmithing) The keeper, or box into which the lock is
      shot. --Knight.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nab
    v 1: tag the base runner to get him out
    2: take into custody; "the police nabbed the suspected
       criminals" [syn: collar, nail, apprehend, arrest,
       pick up, nab, cop]
    3: seize suddenly