'aptychus' originates from Greek, specifically the word 'aptychēs', where 'a-' meant 'not' and 'ptychē' meant 'fold'.

'aptychus' was adopted into scientific/Latinized usage in paleontology to name the paired calcified plates found in ammonites; the term became established in modern literature in the 19th and 20th centuries.

Initially derived to mean 'not folded' or 'unfolded', the term evolved to refer specifically to the calcified plates (opercular/jaw elements) associated with ammonites.