nautiloidPronunciation: /ˈnɔːtɪlɔɪd/Definition of nautiloid noun Zoology a mollusc of a group of mainly extinct marine molluscs which includes the pearly nautilus. Subclass Nautiloidea, class Cephalopoda: Nautilus is the only surviving genus Origin: mid 19th century: from the modern Latin genus name Nautilus (see nautilus)nautiloid in other Oxford dictionaries Definition of nautiloid in the US English dictionary