We have put together a list of words that are similar to FIENDISH.

8 Alternative Words Similar to fiendish

1 Demonic Adjective      Synonym Words Like Demonic
2 Diabolic Adjective      Synonym Words Like Diabolic
3 Diabolical Adjective      Synonym Words Like Diabolical
4 Hellish Adjective      Synonym Words Like Hellish
5 Infernal Adjective      Synonym Words Like Infernal
6 Satanic Adjective      Synonym Words Like Satanic
7 Unholy Adjective      Synonym Words Like Unholy
8 Evil Adjective      Similar Words Like Evil

7 examples of fiendish

1 satanic cruelty
2 a fiendish despot
3 fires lit up a diabolic scene
4 diabolical sorcerers under the influence of devils
5 hellish torture
6 infernal instruments of war
7 unholy grimaces

7 definitions of fiendish

1 Like a fiend; diabolically wicked or cruel; infernal; malignant; devilish; hellish.
2 extremely evil or cruel; expressive of cruelty or befitting hell
3 Of, relating to, or suggestive of a fiend; diabolical.
4 Extremely wicked or cruel.
5 Extremely bad, disagreeable, or difficult: a fiendish blizzard; a fiendish problem.
6 Having the qualities of a fiend; characteristic of a fiend; demoniacal; extremely wicked, cruel, or malicious; devilish: as, a fiendish persecutor; fiendish laughter.
7 Sinister; evil; conniving; in the manner of a fiend.
We get our data from many different dictionaries across the web:
Wordnik, Wiktionary, Century, American Heritage, Gcide