nauta

Nauta, nautae, m., first declension in shape and masculine in fact. This is the small class that catches everyone out: nauta, poeta, agricola, scriba all decline like puella and all take masculine adjectives, so it is bonus nauta and never bona nauta. Declension tells you the endings; it does not tell you the gender.

The word is borrowed from Greek nautes and shortened from an older navita, which is why it sits beside navis so obviously. English took nautical, astronaut and aeronaut from the same Greek root rather than from the Latin.