granule

(grănˈyo͞ol)

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.