The Collaborative International Dictionary of English v.0.48:

Holdup \Hold"up\ (h[=o]ld"[u^]p`), n.
   1. a robbery, usually at gunpoint.
      [PJC]

   2. a delay. "What's the holdup?"
      [PJC]

   3. highway robbery[2].
      [PJC]

WordNet (r) 3.0 (2006):

holdup
    n 1: robbery at gunpoint [syn: armed robbery, heist,
         holdup, stickup]
    2: the act of delaying; inactivity resulting in something being
       put off until a later time [syn: delay, holdup]