NOUN (3)

1. the activity of gathering livestock together so that they can be counted or branded or sold;

2. a summary list; as in e.g. "a news roundup";

3. the systematic gathering up of suspects by the police;
- Example: "a mass roundup of suspects"

The Collaborative International Dictionary of English v.0.48:

Round-up \Round"-up`\, n.
   1. The act of collecting or gathering together scattered
      cattle by riding around them and driving them in. [Western
      U.S.]
      [1913 Webster]

   2. A rounding up, or upward curvature or convexity, as in the
      deck of a vessel.
      [Webster 1913 Suppl.]

   2. A gathering in of scattered persons or things; as, a
      round-up of criminals. [Colloq., U. S.]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

roundup
    n 1: the activity of gathering livestock together so that they
         can be counted or branded or sold
    2: a summary list; as in e.g. "a news roundup"
    3: the systematic gathering up of suspects by the police; "a
       mass roundup of suspects"