Diatom (noun)

1. A type of microscopic single-celled algae with a siliceous cell wall, found in both freshwater and marine environments.
2. A fossilized shell of a diatom, commonly found in sedimentary rocks.

Origin:

Derived from the greek word 'diatome' meaning 'cut in two'.

Examples:

1. Diatoms are an important source of food for many aquatic organisms.
2. Diatoms are known for their intricate and delicate cell wall patterns.
3. The study of diatoms is an important aspect of phycology, the study of algae.
4. The diatom fossils were commonly used to determine the age of sedimentary rock formations.
5. Diatoms play a crucial role in the global carbon cycle and contribute significantly to oceanic primary production.