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, brilliant 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.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.