the.com/airline

means A company that operates aircraft to transport passengers or cargo between destinations on a scheduled or chartered basis.

from A straightforward 19th-century compound of 'air' and 'line' — 'line' in the old sense of a shipping or transport route, the same sense that gave us 'railway line' or 'steamship line.' Once engines could reliably keep machines aloft, the word simply slotted into an existing pattern: whatever carries freight and passengers on a fixed route gets called a 'line,' and this one happened to run through the sky.