hydrofoil hydrofoil /ˈhaɪdrəˌfɔɪl/

noun

1. A speedboat that is equipped with winglike structures that lift it so that it skims the water at high speeds  ( hydrofoil , hydroplane )
   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
   the museum houses a replica of the jet hydroplane that broke the record
   
   
2. 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  ( foil , hydrofoil )
   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
   the fins of a fish act as hydrofoils