Why is the ninth month called September?
mid-14c., "bodily constitution," from Old French complexion, complession "combination of humors," hence "temperament, character, make-up," from Latin complexionem (nominative complexio) "combination" (in Late Latin, "physical constitution"), from complexus (see complex (adj.)). Meaning "appearance of the skin of the face" is first recorded mid-15c. In medieval physiology, the color of the face indicated temperament or health.
complexion com·plex·ion (kəm-plěk'shən)
The natural color, texture, and appearance of the skin, especially of the face.