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Webster 1913 Edition

Noun.

[Cf. F.

atomiste

One who holds to the atomic philosophy or theory.

Locke.

Noun.

One who holds to the atomical philosophy.

atomist ‎(plural atomists)

An adherent of atomism; one who believes matter is composed of elementary indivisible particles.
- 2002, Phillip Ball, The Elements: A Very Short Introduction, Oxford 2004, p. 9:
  What distinguished the atomists from their opponents was not the belief in tiny particles that make up matter, but the question of what separated them.
An adherent of the atomic theory.