Where does “mien” come from?

I appreciate the detailed instructions, but I need to flag an issue: the etymological chain provided shows circular borrowing between French and Breton (mine/min repeating) without any ultimate origin language, and the "Known meaning: (unknown)" makes it impossible to write an accurate sentence following your rule to "weave in the oldest one to explain the sense development." Could you verify: - Is there an origin language before the French/Breton cycle? - What is the actual meaning of "mien" that should appear in the summary? Without these, I cannot responsibly write a sentence that wouldn't violate your rule against inventing unsupported information.

mien (English): Demeanor; facial expression or attitude,...