The Collaborative International Dictionary of English v.0.48:

Round up \Round up"\, v. t.
   to collect or gather together scattered animals, persons, or
   things. "Round up the usual suspects." --[Casablanca]
   [PJC]

WordNet (r) 3.0 (2006):

round up
    v 1: seek out and bring together; "round up some loyal
         followers"

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "round up":
   accumulate, agglomerate, aggregate, aggroup, amass, assemble,
   batch, bring together, bulk, bunch, bunch together, bunch up, cage,
   clump, cluster, collect, colligate, collocate, combine, compare,
   compile, conglomerate, corral, cull, cumulate, dig up,
   draw together, dredge up, drive, drive together, drove, gather,
   gather in, gather together, get in, get together, glean, goad,
   group, grub, grub up, herd, join, juxtapose, lash, lump together,
   make up, mass, match, mobilize, muster, pair, partner, pick,
   pick up, pluck, prick, punch cattle, put together, raise, rake up,
   rally, ride herd on, scare up, scrape together, scrape up,
   shepherd, spur, take up, whip, whip in, wrangle