Abbott-Smith Manual Greek Lexicon
ἀήρ (G109)
7 ἀήρ , ἀέρος, ὁ , [in LXX: II Ki 22:12 (= Ps 17 (18):11 שׁחק ), Wi 8 ;] in Hom., Hes., the lower air which surrounds the earth, as opp. to the purer αἰθήρ of the higher regions; generally, air (MM, VGT , s.v.): Ac 22:23 , I Th 4:17 , Re 9:2 16:17 ; of the air as the realm of demons, Eph 2:2 ; ἀ. δέρειν , of striving to no purpose, I Co 9:26 ; εἰς ἀ. λαλεῖν , of speaking without effect, not being understood, I Co 14:9 .†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain