late 13c. (attested in Anglo-Latin from late 12c.), from Old French pilori "pillory" (mid-12c.), related to Medieval Latin pilloria, of uncertain origin, perhaps a diminutive of Latin pila "pillar, stone barrier" (see pillar), but OED finds this proposed derivation "phonologically unsuitable."

c.1600, from pillory, n.. Figurative sense of "expose publicly to ridicule or abuse" is from 1690s. Related: Pilloried.