1940s; earliest use found in Transactions of the Royal Society of Edinburgh. From ancient Greek πτύγμα fold, anything folded (from the stem of πτύσσειν to fold + -μα), after ptygmatic.
Definition of ptygma in US English:
ptygma
nounˈtɪɡmə
Geology
A ptygmatic fold.
Origin
1940s; earliest use found in Transactions of the Royal Society of Edinburgh. From ancient Greek πτύγμα fold, anything folded (from the stem of πτύσσειν to fold + -μα), after ptygmatic.