Shank

A shank is a slang term for an improvised knife or dagger.

Battlefield 4
"An improvised melee weapon for taking down enemies in close quarters and steal (sic) their dogtags."

- Customization menu description (alpha gameplay)

The Shank is introduced in Battlefield 4 as a choice of melee weapon. It is expected to be distinct from the normal combat knife, if only cosmetically.