run-of-the-mine vs run-of-the-mill

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

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

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

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

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

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