unimagined vs undreamed

unimagined and undreamed both are adjectives.

Word	Noun	Adjective	Verb	Adverb
unimagined	No	Yes	No	No
undreamed	No	Yes	No	No

As adjectives, unimagined and undreamed are synonyms defined as:

Other synonyms of unimagined include undreamed of, undreamt, undreamt of.

unimagined (adjective)	undreamed (adjective)
not imagined even in a dream	not imagined even in a dream