mid-15c. "swear falsely" (implied in perjured; late 13c. in Anglo-French), from Old French parjurer "to break one's word, renege on a promise" (11c.), from Latin periurare "to swear falsely, break one's oath," from per "away, entirely" (see per) + iurare "to swear" (see jury (n.)). Reflexive sense, "make (oneself) guilty by testifying falsely" is from 18c.