Navis, Navis /ˈnaː.wis/ (f) noun; 3rd declension (i stem)
It’s where we get our terms for Navy, Nautical, and Naval. Though the identical “Naus” from Greek may have played a role in it as well. Either way, it means Ship. NOT Navy. Despite it being a feminine noun, Navis isn’t the reason why we call ships “she”.