People:
* Actor
* Actress
* Adult
* Artist
* Athlete
* Author
* Astronaut
Places:
* Airport
* Apartment
* Arch
* Arena
* Avenue
Things:
* Apple
* Airplane
* Animal
* Ant
* Arm
* Arrow
* Art
* Article
* Atom
Concepts:
* Advice
* Age
* Air
* Answer
* Area
* Art
* Attention
Other:
* Afternoon
* Afternoon
* Angle
* Announcement
This is just a small sample, there are many more common nouns starting with "a"!