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]

Moby Thesaurus II by Grady Ward, 1.0:

123 Moby Thesaurus words for "holdup":
   afterthought, armed robbery, arrest, arrestation, arrestment,
   asportation, assault and robbery, banditry, bank robbery, bind,
   block, blockage, blocking, bureaucratic delay, cattle lifting,
   cattle stealing, check, clogging, closing up, closure,
   constriction, cramp, dead time, deceleration, delay, delayage,
   delayed reaction, detainment, detention, double take, drag,
   dragging, ease-off, ease-up, exploitation, extortion, fixation,
   flagging, foot-dragging, gain, halt, hampering, hang-up, heist,
   highway robbery, hijacking, hindering, hindrance, holdback,
   hysteresis, impediment, inhibition, interference, interim,
   interruption, jam, lag, lagging, let, letdown, letup,
   loan-sharking, logjam, minus acceleration, moratorium, mugging,
   negativism, nuisance value, obstruction, obstructionism, occlusion,
   opposition, output lag, overassessment, overcharge, paperasserie,
   pause, pocket picking, process lag, purse snatching, red tape,
   red-tapeism, red-tapery, repression, reprieve, resistance, respite,
   restraint, restriction, retardance, retardation, retardment,
   robbery, robbing, setback, shylocking, slack-up, slackening,
   slow-up, slowdown, slowing, slowing down, slowness, slowup,
   squeeze, stay, stay of execution, stickup, stickup job, stop,
   stoppage, stranglehold, stricture, suppression, surcharge,
   suspension, throughput, tie-up, time constants, time lag,
   time lead, usury, wait