undreamt of vs unimagined

undreamt of and unimagined both are adjectives.

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

As adjectives, undreamt of and unimagined are synonyms defined as:

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

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