diatom

noun

1. Any of a group of minute unicellular algae having a siliceous covering of great delicacy, now categorized as class Diatomophyceae or division Bacillariophyta.

   “Diatoms are enclosed in two shells that fit together like a pillbox.”

   “Diatoms are characterized by a cell wall called a fistula made of silica, which usually has two overlapping sections.”

2. A molecule composed of two atoms of the same element; a homonuclear diatomic molecule.

   “We show here, through a systematic study of the covalent chemical bond covering the entire periodic system, that the maximum bond multiplicity is six. The maximum value is reached by the tungsten diatom, W₂. No other pair of atoms in the periodic system (atomic numbers smaller than about 100) reaches a higher bond order.”