Heavy Finesse Master

You've learned how to use even some of the heaviest weapon's weight gracefully in combat.

Choose one martial weapon that doesn't already have the finesse property, other than the Greatxe/Greatsword/Lance/Maul/Morningstar/Warhammer. While you have that weapon equipped, it gains the finesse property. 

When you roll to hit with an attack given the finesse property via this feat, you get a -1 to hit. (You still add your proficiency and dexterity bonus to this roll.)