Why is the ninth month called September?
c.1400, "action of prostrating oneself," from Old French prostracion (14c.) or directly from Late Latin prostrationem (nominative prostratio), noun of action from past participle stem of prosternere (see prostrate (v.)); or else a native formation from prostrate (v.). Meaning "weakness, exhaustion, dejection" is from 1650s.
prostration pros·tra·tion (prŏ-strā'shən)
Total exhaustion or weakness; collapse.