The word is a combination of: Hydro + Foil
Hydro: relating to water + Foil: a surface, as a wing, designed to aid in lifting or controlling an aircraft by making use of the air currents through which it moves.
A hydrofoil is a wing shape attached to a boat. The foils are shaped like an airplane wing, in that it is tapered to allow water to flow quickly over it. At higher speeds, this action creates lift. This, in effect, lifts the boat out of the water and into the air, where there is much less resistance and higher speeds can be reached.
As mechanical engineering students at the Massachusetts Institute of Technology (MIT) explain:
When a normal boat moves forward, most of the energy expended goes into moving the water in front of the boat out of the way (by pushing the hull through it). Hydrofoils lift the hull out of the water so that you only have to overcome the drag on the foils instead of all of the drag on the hull.
One of the earliest hydrofoil accounts is credited to Thomas Moy, an English engineer who in 1861 installed a set on a boat in the Surrey Canal and noted that when the vessel was towed, it was lifted ‘quite out of the water’.
William Meacham explained the principal and described his own experiments in a March 1906 edition of Scientific American magazine.
That same year in Italy, Enrico Forlanini is seen racing his hydrofoil craft across Lake Maggiore.
Alexander Graham Bell undoubtedly read Meacham’s article. By 1906, Bell was using floats on some tetrahedral kite experiments for trials over water at Beinn Bhreagh.