dreadful vs unspeakable

dreadful and unspeakable both are adjectives.

Word	Noun	Adjective	Verb	Adverb
dreadful	No	Yes	No	No
unspeakable	No	Yes	No	No

As adjectives, dreadful and unspeakable are synonyms defined as:

Other synonyms of dreadful include abominable, atrocious, awful, painful, terrible.

dreadful (adjective)	unspeakable (adjective)
causing fear or dread or terror	exceptionally bad or displeasing
exceptionally bad or displeasing	defying expression or description
extremely disagreeable and unpleasant	too sacred to be uttered