Of air: thin, rarefied. Obsolete.

Esp. of a gas or liquid: thin (in consistency); not dense; not viscous; clear. Also: penetrating or pervasive by reason of lack of density. See also…

Esp. of air, a gas, etc.: thinner or less dense than usual.

Having a thin consistency; rarefied; pervasive; = subtle, adj. 11. Cf. subtile matter n. at compounds 2.

Of a liquid or a pasty substance: Of slight density or consistence; fluid; of air or vapour: not dense; rare, tenuous, subtile. Opposed to thick, adj.…

Of the air: Light; not oppressive. Obsolete. rare.

Of the air: clear, still, pure. Obsolete.