unfathomable vs abysmal

unfathomable and abysmal both are adjectives.

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

As adjectives, unfathomable and abysmal are synonyms defined as:

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

Other synonyms of unfathomable include abyssal.

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