For future reference, OED:

atheism, n.
[…]
Disbelief in, or denial of, the existence of a God. Also, Disregard of duty to God, godlessness (practical atheism).

agnosticism, n.
[…]
The doctrine or tenets of agnostics with regard to the existence of anything beyond and behind material phenomena or to knowledge of a First Cause or God.

agnostic, n. and adj.
[…]

A. n.
1. A person who believes that nothing is known or can be known of immaterial things, especially of the existence or nature of God. Distinguished from atheist n.

2. In extended use: a person who is not persuaded by or committed to a particular point of view; a sceptic. Also: person of indeterminate ideology or conviction; an equivocator.

B. adj.
1. Of or relating to the belief that the existence of anything beyond and behind material phenomena is unknown and (as far as can be judged) unknowable. Also: holding this belief.

2.
a. In extended use: not committed to or persuaded by a particular point of view; sceptical. Also: politically or ideologically unaligned; non-partisan, equivocal.

atheist, n. and adj.
[…]
A. n.

1. One who denies or disbelieves the existence of a God.

2. One who practically denies the existence of a God by disregard of moral obligation to Him; a godless man.

B. adj.

Atheistic, impious.