- a mollusk of the subclass Nautiloidea, including nautiluses and many fossil species that were abundant in the Ordovician and Silurian periods.
- noting or pertaining to a nautiloid.
- any mollusc of the Nautiloidea, a group of cephalopods that includes the pearly nautilus and many extinct forms
- of, relating to, or belonging to the Nautiloidea
- Any of various cephalopod mollusks of the subclass Nautiloidea, having a straight or coiled shell divided internally into a series of chambers of increasing size connected by a central tube. The nautiloids include the modern nautiluses as well as numerous extinct species dating back as far as the Cambrian Period.