from The Century Dictionary.
- noun A name sometimes given to a spirit-level (which see).
- noun A level or airway of former workings made use of in subsequent deeper mining operations for ventilating purposes.
Sorry, no etymologies found.
He spread his wings fully and did not move them as he climbed from air-level to air-level, but his long forked tail expanded and closed continuously.
The air-level guidelines set by the E.P.A. take these factors into account and are more protective for younger classes than older ones.