(strictly) A person who believes that no deities exist (especially, one who has no other religious belief).

Of or relating to atheists or atheism; atheistic.

(transitive, very rare) To make someone an atheist.

The mass of an atom. / (proscribed) atomic weight; the average mass of atoms of an element.

(music) Lacking a tonal center or key. / (linguistics) Not tonal, lacking tones.

(transitive, intransitive) To make reparation, compensation, amends or satisfaction for an offence, crime, mistake or deficiency.

A participant in a group of sporting activities which includes track and field, road running, cross country running and racewalking.

(transitive, idiomatic, archaic) To attack; to engage in combat with. / (transitive, figuratively) To take on; to begin dealing with.

(idiomatic) Even under the most favourable conditions.

randomly, haphazardly