The Collaborative International Dictionary of English v.0.48:

Coarctation \Co`arc*ta"tion\, n. [L. coarctatio.]
   1. Confinement to a narrow space. [Obs.] --Bacon.
      [1913 Webster]

   2. Pressure; that which presses. [Obs.] --Ray.
      [1913 Webster]

   3. (Med.) A stricture or narrowing, as of a canal, cavity, or
      orifice.
      [1913 Webster]

WordNet (r) 3.0 (2006):

coarctation
    n 1: tight or narrow compression [syn: constriction,
         coarctation]
    2: (biology) a narrowing or constriction of a vessel or canal;
       especially a congenital narrowing of the aorta