A.to be like air, Secund.Sent.4; hence,
1. to be thin as air, Dsc.1.68.6.
2. to be light blue (or perh. grey, cloudy), of μολύβδαινα, Id.5.85; of cataract, Dem. Ophth. ap. Aët.7.53; of a kind of jasper, Plin.HN37.115, PMag.Leid.V.6.28.
II. 'tread on air', of boxers, Philostr.Gym.50.