Air

the atmosphere, as opposed to the higher regions of the sky (1
Thess. 4:17; Rev. 9:2; 16:17). This word occurs once as the
rendering of the Hebrew "ruah" (Job 41:16); elsewhere it is the
rendering of "shamaiyim", usually translated "heavens."

The expression "to speak into the air" (1 Cor. 14:9) is a
proverb denoting to speak in vain, as to "beat the air" (1 Cor.
9:26) denotes to labour in vain.