\Di"a*tom\, n. [Gr. ? cut in two. See {Diatomous}.]
1. (Bot.) One of the Diatomace[ae], a family of minute
   unicellular Alg[ae] having a siliceous covering of great
   delicacy, each individual multiplying by spontaneous
   division. By some authors diatoms are called
   Bacillari[ae], 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.