The Collaborative International Dictionary of English v.0.48:

Gibraltar \Gi*bral"tar\, n.
   1. A strongly fortified town on the south coast of Spain,
      held by the British since 1704; hence, an impregnable
      stronghold.
      [Webster 1913 Suppl.]

   2. A kind of candy sweetmeat, or a piece of it; -- called, in
      full, Gibraltar rock.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Gibraltar
    n 1: location of a colony of the United Kingdom on a limestone
         promontory at the southern tip of Spain; strategically
         important because it can control the entrance of ships into
         the Mediterranean; one of the Pillars of Hercules [syn:
         Gibraltar, Rock of Gibraltar, Calpe]