1. [n]  a speedboat that is equipped with hydrofoils 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"
2. [n]  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"

HYDROFOIL is a 9 letter word that starts with H.