D defs.my
Entry 2 senses Webster, 1913

Diatom

/(dī`ȧ*tŏm)/ · Di·a·tom · IPA /ˈdaɪ.əˌtɔm/
01 n. One of the Diatomaceæ, a family of minute unicellular Algæ having a siliceous covering of great delicacy, each individual multiplying by sp…
  1. 1.
    One of the Diatomaceæ, a family of minute unicellular Algæ having a siliceous covering of great delicacy, each individual multiplying by spontaneous division. By some authors diatoms are called Bacillariæ, but this word is not in general use.(Bot.) Also: Bacillariæ
  2. 2.
    A particle or atom endowed with the vital principle.
    “The individual is nothing. He is no more than the diatom, the bit of protoplasm.” — Mrs. E. Lynn Linton.