Common Words:
* attract
* attend
* attempt
* attack
* attain
* attitude
* attractive
* attention
* attitude
* athlete
* atomic
* atrocious
Less Common Words:
* atavism
* at bay
* at odds
* at random
* at rest
* at stake
* at the helm
* at war
* at will
Words with "at" as part of a larger prefix:
* attach (from "ad-")
* attenuate (from "ad-")
* attribute (from "ad-")
Please note: "At" can sometimes be a preposition, not a prefix.