a slang shortening of proper respects (or something similar), c. 1999; see proper. As the nickname of the properties manager of a theater by 1831 (see prop (n.2)). Also the name of a gambling game played with shells in vogue in the 1850s, especially in Boston.
It was, in effect, a crude sort of dice-throwing. Small shells were partially ground down and their hollows filled with sealing-wax. Four of these shells were shaken in the hand and thrown on a table, the stake being won or lost according to the number of red or white sides coming up. [Century Dictionary]