noun
1. : a straight line through the air between two points that disregards irregularities of the intervening ground or space : beeline ; also : a great-circle arc between two points on the earth's surface
2. : a pipe or hose used to supply air under pressure (as to a pneumatic tool or to a diver under water)
3. usually airline ˈ ̷ ̷ˌ ̷ ̷ : an established system of aerial transportation, its equipment, or the organization owning or operating it