/band"wag'euhn/ , n.
1. a wagon, usually large and ornately decorated, for carrying a musical band while it is playing, as in a circus parade or to a political rally.
2. a party, cause, movement, etc., that by its mass appeal or strength readily attracts many followers: After it became apparent that the incumbent would win, everyone decided to jump on the bandwagon.
[ 1850-55, Amer.; BAND 1 + WAGON ]