Why is the ninth month called September?
1530s, "to poke with a stick," of uncertain origin; possibly [Barnhart] a variant of brod, from Middle English brodden "to goad," from Old Norse broddr "shaft, spike" (see brad), or perhaps imitative [OED]. Figurative sense is recorded from 1871. Related: Prodded; prodding.
1787, "pointed instrument used in prodding;" 1802, "act of prodding;" from prod (v.).