What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
Originally: a primitive or ancestral gymnosperm. Now: specifically any of a group of sporogenous fossil plants having secondary wood resembling that of gymnosperms.
Late 19th century; earliest use found in Nature: a weekly journal of science. From pro- + gymnosperm, probably after French progymnosperme.