Other forms: church keys
A church key is a can opener that has a triangular pointed end. You might want to poke two holes in the top of your pineapple juice can with your church key before serving it.
Originally, church keys actually resembled large keys (thus the name) and were used to pry open caps or corks from bottles. Then, when beer cans began being marketed in the 1930s with flat metal covers, the same name, church key, was given to the devices used to open them by piercing them with triangle-shaped holes. These are the type of church keys we still use today, although often our modern church keys also have one end to pop off bottle caps as well.