unimagined vs undreamt

unimagined and undreamt both are adjectives.

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

As adjectives, unimagined and undreamt are synonyms defined as:

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

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