Webster’s Revised Unabridged Dictionary · 1913
Ping-pong
Ping′-pong′, n. [Imitative.] 1. An indoor modification of lawn tennis played with small bats, or battledores, and a very light, hollow, celluloid ball, on a large table divided across the middle by a net.
2. A size of photograph a little larger than a postage stamp.
Ping′-pong′, v. i. To play ping-pong.