Also, before a vowel, hypn-
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'hypno-'< Gr hypnos, sleep < IE *supnos < base *swep-, to sleep > L sopire, to lull to sleep, OE swefan, to sleep