fiendish

Austere is a related term of fiendish.

As adjectives the difference between austere and fiendish

is that austere is austere while fiendish is sinister; evil; conniving; in the manner of a fiend.

Sullen is a related term of fiendish.

As adjectives the difference between sullen and fiendish

is that sullen is having a brooding ill temper; sulky while fiendish is sinister; evil; conniving; in the manner of a fiend.

As a noun sullen

is (obsolete) one who is solitary, or lives alone; a hermit.

Fiendish is a related term of resolute.

As adjectives the difference between fiendish and resolute

is that fiendish is sinister; evil; conniving; in the manner of a fiend while resolute is firm, unyielding, determined.

Vile is a related term of fiendish.

As adjectives the difference between vile and fiendish

is that vile is morally low; base; despicable while fiendish is sinister; evil; conniving; in the manner of a fiend.

Brutish is a related term of fiendish.

As adjectives the difference between brutish and fiendish

is that brutish is of, or in the manner of a brute while fiendish is sinister; evil; conniving; in the manner of a fiend.

Malignant is a related term of fiendish.

As adjectives the difference between malignant and fiendish

is that malignant is harmful, malevolent, injurious while fiendish is sinister; evil; conniving; in the manner of a fiend.

As a noun malignant

is .

Fiendish is a related term of determined.

As adjectives the difference between fiendish and determined

is that fiendish is sinister; evil; conniving; in the manner of a fiend while determined is decided; resolute, possessing much determination.

As a verb determined is

(determine).

Fiendish is a related term of furious.

As adjectives the difference between fiendish and furious

is that fiendish is sinister; evil; conniving; in the manner of a fiend while furious is transported with passion or fury; raging; violent.

Enormous is a related term of fiendish.

As adjectives the difference between enormous and fiendish

is that enormous is (obsolete)  deviating from the norm; unusual, extraordinary while fiendish is sinister; evil; conniving; in the manner of a fiend.

Fiendish is a related term of demonic.

As adjectives the difference between fiendish and demonic

is that fiendish is sinister; evil; conniving; in the manner of a fiend while demonic is pertaining to demons or evil spirits; demoniac.