Why is the ninth month called September?
c.1300, "formal written statement," especially, in civil law, "plaintiff's statement of charges" (mid-14c.); from Old French libelle (fem.) "small book; (legal) charge, claim; writ; written report" (13c.), from Latin libellus "a little book, pamphlet; petition, written accusation, complaint," diminutive of liber "book" (see library). Broader sense of "any published or written statement likely to harm a person's reputation" is first attested 1630s.
mid-15c., "make an initial statement setting out a plaintiff's case" (modern sense from 1560s), from libel (n.), q.v. for sense development. Related: Libeled; libelled; libeling; libelling.