noun.
Any of various microscopic one-celled or colonial heterokonts of the class Bacillariophyceae that are photosynthetic, have a silica cell wall made up of two interlocking parts, and form an important component of phytoplankton.
The Century Dictionary and Cyclopedia
noun.
A member of the Diatomaceæ;
the GNU version of the Collaborative International Dictionary of English
noun.
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.
noun.
A particle or atom endowed with the vital principle.