rankle

Rankle is a verb meaning "to irritate." It entered English most immediately from the Old French verb rancler, which itself was formed from the Old French noun draoncle meaning "festering sore." That noun had come from the Latin noun dracunculus meaning "little snake" (the -culus ending is a diminutive added on to the Latin word for snake, draco, draconis). So when something rankles you, think of it as a little snake nipping at you. (Surely that's better than thinking of something that rankles you as a festering sore?)

And, FYI, the dropping of the d- in the move from draoncle to rancler is an example of the linguistic phenomenon known as aphaeresis--the loss of one or more letters or sounds at the beginning of a word.

Source for etymology of rankle: Chambers Dictionary of Etymology