Of, relating to, or suggestive of a fiend; diabolical.(adjective)
Extremely wicked or cruel.(adjective)
Extremely bad, disagreeable, or difficult: a fiendish blizzard; a fiendish problem. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "fiendish" in a sentence
"It was a high-pitched laugh and if a sound ever deserved to be called fiendish that one did."
"It bore an expression which might truly be called fiendish, for it gave the idea of mental power, of cruelty, of malice, of intense -- of supreme despair."
"Remembering how white soldiers from eastern cities took the skin of a native chief for a trophy of victory, and recalling the fiendish glee of Mandanes over a victim, I can only conclude that neither race may blamelessly point the finger of reproach at the other."