[ 'amənʌɪt ]
■ noun Palaeontology an extinct marine cephalopod mollusc with a flat-coiled spiral shell, found as fossils chiefly in Jurassic and Cretaceous deposits.
Derivatives
ammonoid noun
Origin
C18: from mod. L. ~s , from med. L. cornu Ammonis 'horn of Ammon' (see ammonia ).