abysmal vs unfathomable

abysmal and unfathomable both are adjectives.

Word	Noun	Adjective	Verb	Adverb
abysmal	No	Yes	No	No
unfathomable	No	Yes	No	No

As adjectives, abysmal and unfathomable are synonyms defined as:

abysmal and unfathomable: resembling an abyss in depth; so deep as to be unmeasurable

Other synonyms of abysmal include abyssal.

abysmal (adjective)	unfathomable (adjective)
resembling an abyss in depth; so deep as to be unmeasurable	of depth; not capable of being sounded or measured
very great; limitless	resembling an abyss in depth; so deep as to be unmeasurable
	incapable of being fully understood