nautiloid adjective 2noun 1forms 3 adjective2 •Resembling a nautilus. •Pertaining to the subclass Nautiloidea. noun1 •A mollusc resembling a nautilus; specifically, a cephalopod of the subclass Nautiloidea.Cephalopods have a long fossil record, the earliest certain cephalopod fossils are loosely coiled or straight shelled nautiloids found in the Cambrian of China 515 million years ago. — 2016 formsnautiloids · more nautiloid · most nautiloid