'ammonitic' originates from the word 'ammonite', which is derived from the Latin 'Ammonis cornu', meaning 'horn of Ammon', referring to the Egyptian god Ammon, who was often depicted with ram's horns.

'Ammonis cornu' transformed into the French word 'ammonite', and eventually became the modern English word 'ammonite', from which 'ammonitic' is derived.

Initially, it referred specifically to the horn-like shape of the ammonite fossils, but over time it evolved to describe anything related to or resembling ammonites.