The Collaborative International Dictionary of English v.0.48:

Embargo \Em*bar"go\, n.; pl. Embargoes. [Sp., fr. embargar to
   arrest, restrain; pref. em- (L. in) + Sp. barra bar, akin to
   F. barre bar. See Bar.]
   An edict or order of the government prohibiting the departure
   of ships of commerce from some or all of the ports within its
   dominions; a prohibition to sail.
   [1913 Webster]

   Note: If the embargo is laid on an enemy's ships, it is
         called a hostile embargo; if on the ships belonging to
         citizens of the embargoing state, it is called a civil
         embargo.
         [1913 Webster]