Dictionary.com
definitions

thi-

variant of thio- before a vowel: thiazine.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for thi-

thi-

combining form

a variant of thio-
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
thi- in Medicine

thi-

pref.

Variant ofthio-
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
thi- in Science

thio-

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A prefix that means “containing sulfur,” used especially of a compound in which an oxygen atom has been replaced by a sulfur atom, as in thiourea.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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.