British; blackjack

ETYM French ponton (cf. Italian pontone), from Latin ponto, -onis, from pons, pontis, a bridge, perhaps originally, a way, path: cf. Skr. path, pathi, panthan. Related to Punt a boat.
1. A float supporting a seaplane.
2. A floating structure (as a flat-bottomed boat) that serves as a dock or to support a bridge.