1. adulterate - To make impure by the admixture of other or baser ingredients.
2. adumbrate - To represent beforehand in outline or by emblem.
3. advent - The coming or arrival, as of any important change, event, state, or personage.
4. adverse - Opposing or opposed.
5. adversity - Misfortune.
6. advert - To refer incidentally.
7. advertiser - One who advertises, especially in newspapers.
8. advisory - Not mandatory.
9. advocacy - The act of pleading a cause.
10. advocate - One who pleads the cause of another, as in a legal or ecclesiastical court.
11. aerial - Of, pertaining to, or like the air.
12. aeronaut - One who navigates the air, a balloonist.
13. aeronautics - the art or practice of flying aircraft
14. aerostat - A balloon or other apparatus floating in or sustained by the air.
15. aerostatics - The branch of pneumatics that treats of the equilibrium, pressure, and mechanical properties.