- airThe substance constituting Earth's atmosphere: a gaseous mixture of nitrogen, oxygen, and various trace gases.
- ariaA musical piece written typically for a solo voice with orchestral accompaniment in an opera or cantata.
- aerobicLiving or occurring only in the presence of oxygen e.g. aerobic bacteria.
- aerostatAn aircraft, such as a dirigible or balloon, that derives its lift from buoyancy rather than from wings or rotors.
- aeroscepsisThe observation or examination of the air via specialized organs.