an·gos·tu·ra bark 
(ăng′gə-strə, -styrə)
(ăng′gə-strə, -styrə)n.
The bitter aromatic bark of either of two South American trees, Galipea officinalis or Cusparia trifoliata (both sometimes placed in the genus Angostura), used as a flavoring in bitters and as a tonic.
[After Angostura (Ciudad Bolívar), Venezuela.]