Diatom

Part of speech: noun (n.)

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.

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.