An individual of microscopic unicellular algae, the shells of which compose a sedimentary infusorial earth. [G. diatomos, cut in two]
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di·a·tom 'dī-ə-.täm n any of a class (Bacillariophyceae) of minute planktonic unicellular or colonial algae with silicified skeletons that form diatomite
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di·a·tom (diґə-tom) any of numerous unicellular microscopical forms of alga having a wall of silica; authorities disagree as to which phylum of kingdom Protista to put them in. Several species are toxic and can cause the ocean condition called red tide. The skeletal siliceous remains of many others are mined from deposits and used as filtering and abrasive agents. See also infusorial earth, under earth.Medical dictionary. 2011.