Why is the ninth month called September?
Old English hindrian "to harm, injure, impair, check, repress," from Proto-Germanic *hinderojanan (cf. Old Norse hindra, Dutch hinderen, Old High German hintaron, German hindern "to keep back"), from a root meaning "on that side of, behind" (cf. hind (adj.)); thus the ground sense is "to put or keep back," though this sense in English is recorded only from late 14c. Related: Hindered; hindering.
"situated in the rear, toward the back," late 14c., probably from Old English hinder (adv.) "behind, back, afterward," but treated as a comparative of hind (adj.). Related to Old High German hintar, German hinter, Gothic hindar "behind." Middle English had hinderhede, literally "hinder-hood; posterity in time, inferiority in rank;" and hinderling "person fallen from moral or social respectability, wretch."