The Collaborative International Dictionary of English v.0.48:

Angostura \An`gos*tu"ra\, Angostura bark \An`gos*tu"ra
bark"\([aum][ng]`g[o^]s*t[=oo]"r[.a] b[aum]rk`). [From
   Angostura, in Venezuela.]
   A bitter aromatic bark, obtained from a South American tree
   of the rue family (Galipea cusparia, or Galipea
   officinalis). It is used used as a tonic, in medicines,
   liqueurs and bitters. --U. S. Disp.
   [1913 Webster WordNet 1.5]

WordNet (r) 3.0 (2006):

angostura
    n 1: the bitter bark of a South American tree; used in medicines
         and liqueurs and bitters [syn: angostura bark,
         angostura]