Bastard sword

Superior one-handed melee weapon
Cost: 30 gp
Damage: 1d10
Proficient: +3
Weight: 6 lb.

This heavier variation on the longsword requires special training to cope with its weight and peculiar balance. Warriors who master the bastard sword gain the typical sword’s accuracy and balance combined with the striking power of a warhammer or battle axe.

Versatile (Versatile weapons are one-handed, but you can use them two-handed. If you do, you deal an extra 1 point of damage when you roll damage for the weapon.
A Small character such as a halfling must use a versatile weapon two-handed, and doesn’t deal extra damage.

Heavy blade (Blades are balanced edged weapons. Heavy blades share some of the precision of light blades and some of the mass of axes. Heavy blades are used primarily for slashing cuts rather than stabs and thrusts.).

Published in Player's Handbook, page(s) 218, Mordenkainen's Magnificent Emporium, page(s) 21.