Frightful is a synonym of sinister.

In obsolete|lang=en terms the difference between frightful and sinister

is that frightful is (obsolete): full of fright; affrighted; frightened while sinister is (obsolete) wrong, as springing from indirection or obliquity; perverse; dishonest.

As adjectives the difference between frightful and sinister

is that frightful is (obsolete): full of fright; affrighted; frightened while sinister is inauspicious]], ominous, unlucky, illegitimate (as in [[w:bar sinister|bar sinister ).

Desperate is a related term of critical.

As adjectives the difference between desperate and critical

is that desperate is being filled with, or in a state of despair; hopeless while critical is inclined to find fault or criticize; fastidious; captious; censorious; exacting.

As a noun critical is

a critical value, factor, etc.

Jackass is a related term of dunderhead.

As nouns the difference between jackass and dunderhead

is that jackass is a male donkey while dunderhead is a stupid person; a dunce.

As a proper noun jackass

is (poker slang) a jack and an ace as a starting hand in texas hold 'em due to phonetic similarity.

As a verb jackass

is (rare) to behave very obnoxiously.

As adjectives the difference between extensive and huge

is that extensive is in the nature of an extent, wide, widespread while huge is very large.

Affliction is a related term of pest.

As nouns the difference between affliction and pest

is that affliction is a state of pain, suffering, distress or agony while pest is plague.

Deduction is a related term of resolution.

As nouns the difference between deduction and resolution

is that deduction is deduction (all meanings) while resolution is resolution.

Arm is a related term of part.

As nouns the difference between arm and part

is that arm is sleeve; a part of a garment that covers all or part of an arm while part is party (political group).

Imperturbable is a related term of impersonal.

As adjectives the difference between imperturbable and impersonal

is that imperturbable is not easily perturbed, upset or excited while impersonal is not personal; not representing a person; not having personality.

Unambiguously is a related term of frankly.

As adverbs the difference between unambiguously and frankly

is that unambiguously is in a manner that is not ambiguous; leaving no doubt; clearly; certainly while frankly is (lb) in a frank, open or (too) honest manner.

Alternative is a related term of resolution.

As nouns the difference between alternative and resolution

is that alternative is alternative while resolution is resolution.