ponorn.

1890 J. de Asboth Official Tour Bosnia & Herzegovina 322 The Muslitza, which has vanished into the caverns or Ponors, they say, does not reappear until it reaches Trebinje, far away.

1903 C. Black tr. J. F. M. Partsch Central Europe v. 60 Large valleys..which..as a rule are only drained underground through sink-holes. These holes or ‘ponors’ [Ger. Ponore] open sometimes in the midst of the valley,..sometimes even at a distance up the sides.

1937 S. W. Wooldridge & R. S. Morgan Physical Basis Geogr. xix. 290 They [sc. limestone caves] commonly form part of a complex system of channels, widening locally into chambers, and fall broadly into two sets, viz. roughly horizontal galleries, and vertical or steeply inclined shafts, of which the higher members are the ‘ponors’ communicating with the surface.

1971 J. N. Jennings Karst vi. 139 In some poljes certain ponors change function for a period in the wet season and spew out water.

1985 F. Singleton Short Hist. Yugoslav Peoples i. 3 Dolina (literally a valley) is a shallow, saucer-shaped depression, often leading to a sink-hole or ponor.