ˈhɑe.dɹəˌfoɪl ˈhaɪ.dɹoʊˌfɔɪl ˈhaɪdɹəʊˌpleɪn ˈhaɪdɹoʊˌpleɪn a speedboat that is equipped with winglike structures that lift it so that it skims the water at high speeds the museum houses a replica of the jet hydroplane that broke the record a device consisting of a flat or curved piece (as a metal plate) so that its surface reacts to the water it is passing through the fins of a fish act as hydrofoils