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[thal-uh s] /ˈθæl əs/
noun, plural thalli
[thal-ahy] /ˈθæl aɪ/ (Show IPA),
thalluses. Botany, Mycology.
a simple vegetative body undifferentiated into true leaves, stem, and root, ranging from an aggregation of filaments to a complex plantlike form.
Origin of thallus
1820-30; < New Latin < Greek thallós young shoot, twig Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for thalli


noun (pl) thalli (ˈθælaɪ), thalluses
the undifferentiated vegetative body of algae, fungi, and lichens
Derived Forms
thalloid, adjective
Word Origin
C19: from Latin, from Greek thallos green shoot, from thallein to bloom
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 thalli



Latin, from Greek thallos "green shoot, twig," related to thalia "abundance," thalos "scion, child," ultimately from PIE root *dhal- "to bloom" (cf. Old Irish duilesc, a type of algae).

Online Etymology Dictionary, © 2010 Douglas Harper
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thalli in Medicine

thallus thal·lus (thāl'əs)
n. pl. thal·lus·es or thal·li (thāl'ī)
A plant body or fungus undifferentiated into stem, root, or leaf.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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thalli in Science
Plural thalli (thāl'ī)
A type of body found among plants and fungi that is not differentiated into roots, stems, or leaves. Thalli are found among lichens, mosses, liverworts, and many algae, as well as the gametophyte generations of horsetails and ferns, which have rhizoids but not true roots.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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