hiero-

hiero-

or hier-
pref.
Sacred; holy: hierology.

[Greek, from hieros, holy; see eis- in Indo-European roots.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

hiero-

or before a vowel

hier-

combining form
holy or divine: hierocracy; hierarchy.
[from Greek, from hieros]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

hiero-

a combining form meaning “sacred,” “priestly”: hierocracy.
Also, esp. before a vowel, hier-.
[< Greek, comb. form of hierós]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
The prefixes "hiero-" and "hieratic" from <hieros> (holy) usually denoted authority over sacred things, in this case, religious or sacerdotal leadership.