DCHP-1 Online
air-line † Obs. 
1 n. a railway line, especially a through or transcontinental line.
- 1881 The airline between Winnipeg and Portage la Prairie is all under contract, and will be open for traffic on the first of October.
- 1883 The quiet serenity which usually prevails in this peaceful region was disturbed on Friday morning by the shrill whistle of the locomotive and people began to wonder if the South Saskatchewan Valley Railway Company had waked up at last, and sent in a special train over the "air" line with those five hundred navvies who were to have commenced work last June.
2 n. a direct line or route, "as the crow flies"; a beeline.
- 1854 The engineer and his assistants should have seen it, as the road at this place is straight as an air-line.
- 1955 From the Kechika Forks to Icy Cape is about 1,200 miles--also in an air line.
- 1881 The airline between Winnipeg and Portage la Prairie is all under contract, and will be open for traffic on the first of October.