During the Middle Ages, most swords were relatively light. By the 15th century, larger and heavier swords had been developed, including the 'Bastard' or 'Hand-and-a-half' sword. They were hybrid swords that enabled blows to be delivered with the power of a two-handed sword but could also be wielded with one hand.
https://collections.royalarmouries.o...h%20one%20hand.
The versatility of the design prevented the sword from being specifically categorized as either a one-handed or two-handed weapon. The word bastard was therefore to this sword meaning something irregular or inferior or of dubious origin, having a misleading appearance
https://english.stackexchange.com/qu...g%20appearance.
funny that bastard is used as a curse word meaning different father, actually more accurately, born without marriage?