Knife

Knife was a planned move for Tomb Raider III: Adventures of Lara Croft. Lara Croft could use the knife to stab things, and pry secrets out of walls. The knife would be hidden on a leg.

The knife was added in Tomb Raider: The Last Revelation, but not into the hands of the player. It is Werner Von Croy who fights off boars with the knife.

Knife made it's return in Rise of the Tomb Raider, but this time players are the ones who can finally use it, to stealth kill enemies, or cut ropes.

Knife also return in the Shadow of the Tomb Raider where Lara improvised one from the crashed aeroplane's propeller.

Trivia

 * Knife was actually first shown in the cutscenes of Tomb Raider.