undistinguished vs run-of-the-mill

undistinguished and run-of-the-mill both are adjectives.

Word	Noun	Adjective	Verb	Adverb
undistinguished	No	Yes	No	No
run-of-the-mill	No	Yes	No	No

As adjectives, undistinguished and run-of-the-mill are synonyms defined as:

undistinguished and run-of-the-mill: not special in any way; lacking distinction

Other synonyms of undistinguished include mine run, run-of-the-mine, unexceptional.

undistinguished (adjective)	run-of-the-mill (adjective)
not special in any way; lacking distinction	not special in any way; lacking distinction