prong (n.)

1530s, "to poke with a stick," of uncertain origin; possibly [Barnhart, Century Dictionary] a variant of brod, from Middle English brodden "to goad," from Old Norse broddr "shaft, spike" (see brad), or perhaps imitative [OED]. Compare dialectal prog "pointed instrument for poking" (1610s), also as a verb, "to poke about." 

Figurative sense of "mental incitement or instigation" is by 1871. Related: Prodded; prodding.

1520s, "sudden paroxysm of physical pain, acute painful spasm," a word of unknown origin, not found in Middle English. Perhaps it is related to prong (prongys of deth is recorded from mid-15c.). Reference to mental or emotional pain is from 1560s. As a verb, "cause or suffer a pang or pangs," c. 1500. Related: Pangs.