1. A hole to admit or discharge air; specifically, a spot in the ice not frozen over. [ 1913 Webster ]

2. (Founding) A fault in a casting, produced by a bubble of air; a blowhole. [ 1913 Webster ]

3. (Aëronautics) A local region in the atmosphere having a downward movement and offering less than normal support for the sustaining surfaces of a flying machine, causing an airplane to drop suddenly. Same as air pocket. [ Webster 1913 Suppl. ]