Why is the ninth month called September?
Old English bat "boat, ship, vessel," from Proto-Germanic *bait- (cf. Old Norse batr, Dutch boot, German Boot), possibly from PIE root *bheid- "to split" (see fissure), with the sense of making a boat by hollowing out a tree trunk; or it may be an extension of the name for some part of a ship. French bateau "boat" is from Old English or Norse. Spanish batel, Italian battello, Medieval Latin batellus likewise probably are from Germanic.