bachelor (n.)
c.1300, "young man;" also "youthful knight, novice in arms," from Old French bacheler (11c.) "knight bachelor," a young squire in training for knighthood, of uncertain origin, perhaps from Medieval Latin baccalarius "vassal farmer," one who helps or tends a baccalaria "section of land." Or from Latin baculum "a stick," because the squire would practice with a staff, not a sword. Meaning evolved from "knight in training" to "young unmarried man" (early 14c.). Bachelor party as a pre-wedding ritual is from 1882.