A mechanical device for holding or grappling, or, as a verb, the act of so securing.
1. Neufeldt, Victoria, ed. 1994. Webster's New World Dictionary of American English. 3rd College Edition ed. New York: Prentice Hall.
Popular and even professional usage these days tends to be confined to the mechanism which
secures an air- or watertight door or hatch. Submarines are full of them and unless you are a sailor or in a navy, my guess is that, like me, the time you are most likely to hear this kind of dog referred to is in a movie involving submarines: Dog the hatches! Dive! Dive!