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[dahy-uh-tuh m, -tom] /ˈdaɪ ə təm, -ˌtɒm/
any of numerous microscopic, unicellular, marine or freshwater algae of the phylum Chrysophyta, having cell walls containing silica.
1835-45; < Neo-Latin Diatoma originally a genus name, feminine noun based on Greek diátomos cut in two. See dia-, -tome Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Examples from the web for diatoms
  • As they get bigger, they eat protozoa, diatoms and smaller crabs that live on the ocean floor.
  • In particular, the remains of diatoms are a main ingredient in oil.
  • Perhaps someone could fiddle with diatoms to get them to make heavier shells.
  • diatoms, a type of shelled plankton, made their first radiation into the ocean.
  • Trillions of diatoms, zooplankton, and crustaceans pepper the ice column.
  • Millions of years ago, tiny sea creatures called diatoms lived and died in ocean basins.
  • Its frustule is a form of armor that can protect the diatoms from predators.
  • If phosphorus is limiting, the diatoms outcompete the algae, which are phosphorus fumblers.
  • Leave it to the diminutive diatoms to bring out algae's best side.
  • In fact, this sea generates little life beyond single-celled diatoms and tiny dinoflagellates.
British Dictionary definitions for diatoms


/ˈdaɪətəm; -ˌtɒm/
any microscopic unicellular alga of the phylum Bacillariophyta, occurring in marine or fresh water singly or in colonies, each cell having a cell wall made of two halves and impregnated with silica See also diatomite
Word Origin
C19: from New Latin Diatoma (genus name), from Greek diatomos cut in two, from diatemnein to cut through, from dia- + temnein to cut
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for diatoms



1845, coined from Greek diatomos "cut in two," from diatemnein "to cut through," from dia- "through" (see dia-) + temnein "to cut" (see tome). So called because they typically appear to have been cut in half. Related: Diatomic.

Online Etymology Dictionary, © 2010 Douglas Harper
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diatoms in Science
Any of various microscopic protists of the phylum Bacillariophyta that live in both fresh and marine water, have hard bivalve shells (called frustules) composed mostly of silica, and often live in colonies. Most diatoms can perform photosynthesis. They make up a large portion of the marine plankton and are an important food source for many aquatic animals. The skeletal remains of diatoms are the main constituent of diatomite.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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