say it: HAHY-druh-foyl
hydrofoil is a noun meaning "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". It carries 2 recorded senses.
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”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for hydrofoil come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.