The atmosphere, as opposed to the higher regions of the sky (1 Thessalonians 4:17; Revelation 9:2; 16:17). This word occurs once as the rendering of the Hebrew
(Job 41:16); elsewhere it is the rendering of
Shamaiyim , usually translated "heavens."
The expression "to speak into the air" (1 Corinthians 14:9) is a proverb denoting to speak in vain, as to "beat the air" (1 Corinthians 9:26) denotes to labour in vain.
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Air'". "Easton's Bible Dictionary".