1. Opening in the roof of a cave or cavern through which air is expelled vigorously. In coastal areas the phenomenon is usually due to compression of air within the cave by incoming tides or waves . 2. Cliff top entrance to a sea cave, also known as a geo, gloop, or gloup . 3. (Australian.) A small hole in the surface of the Nullarbor Plain through which air blows in and out with observable force, sometimes audibly . Related to breathing hole.Synonyms: (French.) trou souffleur; (German.) Windhohle; (Greek.) ope ekphysosa; (Italian.) bocca soffiante; (Spanish.) soplador; (Turkish.) uflenme agzi; (Yugoslavian.) vjetrenica, veternica, puhaljka, pihalnik, dihalnik. See also steam hole.