What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
1Botany and Mycology. The larger of the two types of spore produced by a heterosporous plant (now usually called megaspore).
2Biology. A large spore (usually the larger of two types of spore) produced by various protoctists.
Mid 19th century; earliest use found in Todd's Cyclopaedia of Anatomy and Physiology. From macro- + spore. Compare French macrospore.