What is an Atheist?

Here is the definition from dictionary.com:

a person who denies or disbelieves the existence of a supreme being or beings.

—Synonyms: Atheist, agnostic, infidel, skeptic refer to persons not inclined toward religious belief or a particular form of religious belief. An atheist is one who denies the existence of a deity or of divine beings. An agnostic is one who believes it impossible to know anything about God or about the creation of the universe and refrains from commitment to any religious doctrine. Infidel means an unbeliever, especially a nonbeliever in Islam or Christianity. A skeptic doubts and is critical of all accepted doctrines and creeds.

Hmmm - sounds like my brother. Do you know anyone like this? Is this definition accurate?