Why is the ninth month called September?
late 14c., from Old French preface "opening part of sung devotions" (14c.) and directly from Medieval Latin prefatia, from Latin praefationem (nominative praefatio) "fore-speaking, introduction," in Medieval Latin "prologue," noun of action from past participle stem of praefari "to say beforehand," from prae "before" (see pre-) + fari "speak" (see fame (n.)).
1610s, from preface (n.). Related: Prefaced; prefacing.