ammonite

noun

am·​mo·​nite ˈa-mə-ˌnīt 

: any of a subclass (Ammonoidea) of extinct cephalopods especially abundant in the Mesozoic age that had flat spiral shells with the interior divided by septa into chambers

ammonitic

ˌa-mə-ˈni-tik 

adjective

Illustration of ammonite

Examples of ammonite in a Sentence

Recent Examples on the Web

By shedding heavy shells like those seen in early nautiloids and ammonites, the ancestors of modern octopuses traded passive defense for active offense. —Jacek Krywko, ArsTechnica, 24 Apr. 2026

Another new display features an ancient sea life diorama that includes Oddball Art Studios’ Mike Rende’s vibrant sculptures of a Tully Monster, an ammonite, an opabinia and a trilobite set up in an underwater scene created by museum board President Judy Hayner. —Mike Danahey, Chicago Tribune, 6 Feb. 2026

Visitors typically find ancient shark’s teeth and internal molds of ammonites and oyster shells. —Mark Price, Miami Herald, 5 Aug. 2025

The biggest of these whale-like creatures were apex predators, hunting ancient fish, ammonites, and even their smaller reptile relatives. —Lauren Leffer, Popular Science, 16 July 2025

Word History

Etymology

borrowed from New Latin ammōnīta or ammōnītēs, from Latin Ammōn, the Egyptian god Ammon (in cornu Ammōnis, a name for the fossils, literally "horn of Ammon," alluding to the ram's head of the god and the hornlike shape of the stones) + -īta, -ītēs -ite entry 1

First Known Use

1726, in the meaning defined above

Rhymes for ammonite

• acolyte
• aconite
• allanite
• alunite
• amberlite
• amorite
• amphitrite
• analyte
• anchorite
• andesite
• anhydrite
• ankerite

Kids Definition

ammonite

noun

am·​mo·​nite ˈam-ə-ˌnīt 

: any of numerous flat spiral fossil shells of mollusks related to the nautilus that are especially abundant in the Mesozoic era of geological history

ammonitic

ˌam-ə-ˈnit-ik 

adjective