1. an evil spirit; devil
2. an inhumanly wicked or cruel person
3. Us, Informal
a. a person addicted to some activity, habit, etc.
⇒ a fresh-air fiend
b. a person who is excellent at some activity
⇒ a fiend at tennis
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 'fiend'ME fend, feend < OE feond, lit., the one hating, orig. prp. < base of feogan, to hate, akin to Goth fijands < fijan, to hate < IE base *pē(i)-, to harm