A fiendish problem or task is very difficult and challenging. the fiendish difficulty of the questions. + fiendishly fiend·ish·ly America's trade laws are fiendishly complex
extremely evil or cruel; expressive of cruelty or befitting hell; "something demonic in him--something that could be cruel"; "fires lit up a diabolic scene"; "diabolical sorcerers under the influence of devils"; "a fiendish despot"; "hellish torture"; "infernal instruments of war"; "satanic cruelty"; "unholy grimaces"
A fiendish plan, action, or device is very clever or imaginative. a fiendish plot. = devilish + fiendishly fiend·ish·ly This figure is reached by a fiendishly clever equation
If you describe someone as a fiend, you mean that they are extremely wicked or cruel. A tearful husband repeated calls for help in catching the fiend who battered his wife. = monster
Primarily refers to baatezu, gehreleths, hordlings, tanar'ri, and yugoloths, but sometimes includes any intelligent being native to the Lower Planes (night hags, imps, quasits, and the like)
a person motivated by irrational enthusiasm (as for a cause); "A fanatic is one who can't change his mind and won't change the subject"--Winston Churchill
Fiend can be used after a noun to refer to a person who is very interested in the thing mentioned, and enjoys having a lot of it or doing it often. if you're a heavy coffee drinker or strong-tea fiend