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[thahy-oh] /ˈθaɪ oʊ/
adjective, Chemistry.
containing sulfur, especially in place of oxygen.
Origin of thio
independent use of thio-


a combining form meaning “sulfur,” used in chemical nomenclature in the names of compounds in which part or all of the oxygen atoms have been replaced by sulfur; often used to designate sulfur analogues of oxygen compounds.
Also, especially before a vowel, thi-.
combining form representing Greek theîon Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for thio
Historical Examples
  • Alum does not agree with the thio dyestuffs which are manufactured by Dahl & Co., Barmin, and are fast against soap and light.

British Dictionary definitions for thio


combining form
indicating that a chemical compound contains sulphur, esp denoting that a compound is derived from a specified compound by the replacement of an oxygen atom with a sulphur atom: thiol, thiosulphate
Word Origin
from Greek theion sulphur
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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thio in Medicine

thio- or thi-
Containing sulfur, used especially of a compound in which oxygen has been replaced by a divalent sulfur: thioacid.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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thio in Science
thio- or thi-  
A prefix that means "containing sulfur," used especially of a compound in which an oxygen atom has been replaced by a sulfur atom, as in thiourea.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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