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[al-jee] /ˈæl dʒi/
plural noun, singular alga
[al-guh] /ˈæl gə/ (Show IPA)
any of numerous groups of chlorophyll-containing, mainly aquatic eukaryotic organisms ranging from microscopic single-celled forms to multicellular forms 100 feet (30 meters) or more long, distinguished from plants by the absence of true roots, stems, and leaves and by a lack of nonreproductive cells in the reproductive structures: classified into the six phyla Euglenophyta, Crysophyta, Pyrrophyta, Chlorophyta, Phaeophyta, and Rhodophyta.
Compare blue-green algae.
Origin of algae
< New Latin, plural of Latin alga seaweed
Related forms
algal, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for algae
Contemporary Examples
Historical Examples
  • As far as they could see there was no algae in sight, the water was one glassy blue.

    The Cruise of the Dry Dock T. S. Stribling
  • The simplest form of vegetation is algae which grows on the sides of the tank.

    Boy Scouts Handbook Boy Scouts of America
  • He regarded a bowl of algae as if about to make it disappear.

  • We've put quite a dent in the algae and synthetics operations in this sector.

    The Lani People J. F. Bone
  • The Carrageen or Iceland moss, or lichen is one of the algae of the sea.

British Dictionary definitions for algae


plural noun (sing) alga (ˈælɡə)
unicellular or multicellular organisms formerly classified as plants, occurring in fresh or salt water or moist ground, that have chlorophyll and other pigments but lack true stems, roots, and leaves. Algae, which are now regarded as protoctists, include the seaweeds, diatoms, and spirogyra
Derived Forms
algal (ˈælɡəl) adjective
Word Origin
C16: from Latin, plural of alga seaweed, of uncertain origin
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 algae

(plural), 1794, from alga (singular), 1550s, from Latin alga "seaweed," of uncertain origin, perhaps from a PIE root meaning "to putrefy, rot."

Online Etymology Dictionary, © 2010 Douglas Harper
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algae in Medicine

algae al·gae (āl'jē)
Any of various chiefly aquatic, eukaryotic, photosynthetic organisms, ranging in size from single-celled forms to the giant kelp.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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algae in Science
Plural algae (āl'jē)
Any of various green, red, or brown organisms that grow mostly in water, ranging in size from single cells to large spreading seaweeds. Like plants, algae manufacture their own food through photosynthesis and release large amounts of oxygen into the atmosphere. They also fix large amounts of carbon, which would otherwise exist in the atmosphere as carbon dioxide. Algae form a major component of marine plankton and are often visible as pond scum and blooms in tidal pools. Land species mostly live in moist soil and on tree trunks or rocks. Some species live in extreme environments, such as deserts, hot springs, and glaciers. Although they were once classified as plants, the algae are now considered to be protists, with the exception of the cyanobacteria, formerly called blue-green algae. The algae do not form a distinct phylogenetic group, but the word alga serves as a convenient catch-all term for various photosynthetic protist phyla, including the green algae, brown algae, and red algae.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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algae in Culture
algae [(al-jee)]

Primitive organisms that contain chlorophyll but do not have structures, such as xylem and phloem, to transport fluids. Algae sometimes contain only a single cell, and nowadays they are not considered members of the plant kingdom.

Note: The most familiar algae are the greenish scum that collects in still water.
Note: Algae supply a considerable part of the world's oxygen.
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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