- aptychusA hard calcareous plate forming part of the body of an ammonite.
- pentaptychA five-part polyptych; a picture, or combination of pictures, consisting of a centrepiece and double folding doors or wings, as for an altarpiece.
- ptychographyA technique that aims to solve the diffraction-pattern phase problem by interfering adjacent Bragg reflections coherently and thereby determining their relative phase.
- ptychonomeAn enclosure formed (of leaves) by some organisms of the order Lepidoptera; a tentiform mine.