Backsword

The backsword is one of the two special items that can be obtained from the box edition of Puzzle Pirates. The other is the savvy hat.

This item cannot be traded or placed in a trade window (for example, to show a friend the drop pattern). Also the backsword cannot be placed in a sword rack. It does not age. Pirates who do not have the box edition may never own a backsword. Pirates who do own the box edition can only obtain one backsword per pirate. Additionally, if a pirate chooses the savvy hat they forfeit the option to obtain the backsword on that particular pirate.

According to Cleaver, the backsword's drop pattern is just okay.

To claim the backsword, register the key code from the box edition of Puzzle Pirates on the account page. From then on, any pirates created under that account will have a new mission called "Claim your inheritance." Select that mission and follow the instructions to claim either the backsword or savvy hat. When the backsword is selected, a randomly-colored backsword is placed in the pirate's Booty panel.

The backsword shares its pattern with the battle axe.

Trivia
According to Wikipedia, the term backsword does not describe a specific sword but instead denotes any sword with only a single edge. For example, a machete is a type of backsword, as is the Japanese katana. The backsword instead resembles a Scottish broadsword, which can be both single- and double-edged.