fiendishly

UK: /ˈfiːndɪʃli/

WordReference Random House Learner's Dictionary of American English © 2026

fiend /find/   n. [countable]

1. any evil spirit;
   demon.
2. an extremely cruel or wicked person.
3. Informal Terms a person who is addicted or very attached to some habit, practice, condition, etc.:
   a fiend for neatness.

fiend•ish, adj. 
fiend•ish•ly, adv. 

WordReference Random House Unabridged Dictionary of American English © 2026

fiend  (fēnd), n. 

1. Satan;
   the devil.
2. any evil spirit;
   demon.
3. a diabolically cruel or wicked person.
4. a person or thing that causes mischief or annoyance:
   Those children are little fiends.
5. Informal Terms a person who is extremely addicted to some pernicious habit:
   an opium fiend.
6. Informal Terms a person who is excessively interested in some game, sport, etc.;
   fan;
   buff:
   a bridge fiend.
7. a person who is highly skilled or gifted in something:
   a fiend at languages.

• bef. 900; Middle English feend, Old English fēond; cognate with German Feind, Old Norse fjandr, Gothic fijands foe, origin, originally present participle of fijan to hate

fiend′like′, adj. 
Synonyms

• 3. monster, savage, brute, beast, devil.

WordReference Random House Unabridged Dictionary of American English © 2026

fiend•ish  (fēn′dish), adj. 

1. diabolically cruel and wicked.

• fiend + -ish¹ 1520–30

fiend′ish•ly, adv. 
fiend′ish•ness. n.