1. A small grain or pellet; a particle.
2. Geology A rock or mineral fragment larger than a sand grain and smaller than a pebble, between 2 and 4 millimeters in diameter.
3. Astronomy One of the small, transient, luminous markings in the photosphere of the sun.
4. Biology A cellular or cytoplasmic particle, especially one that stains readily.
[Late Latin grānulum, diminutive of Latin grānum, grain; see gə-no- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.