bah

Etymology 1

Early 19th century, probably borrowed from French bah.

intj

1. (sometimes humorous) Expressing contempt, disgust, or bad temper.
   "To the doctor's? Bah!" said the sorceress, and spat upon the floor. 1886, Peter Christen Asbjørnsen, translated by H.L. Brækstad, Folk and Fairy Tales, page 301
   Templeton looked over the assembled servants speculatively, then shrugged. "Bah!" he said. "They're of no use to me. Come, Andrew, a word with you upstairs." 1992, April Kihlstrom, Dangerous Masquerade

Etymology 2

noun

1. Alternative spelling of baa (the cry of a sheep or goat).