Shiv

Shiv \shiv\ , noun;
1. A knife, especially a switchblade

Prison shivs and shanks (source)

Shiv dates to 1915 as shive ("a razor"). The Oxford English Dictionary lists it as equal to chiv(e), which means "a knife" and is considered "Thieves' Cant," which is a secret language used by thieves, beggars and various kinds of hustlers.  It's a type of argot, which is "the jargon, slang, or peculiar phraseology of a class." Argots are a distinct form of jargon and slang that is generally secretive in nature and lets group insiders speak openly to one another without worrying about outsiders understanding them.