noun

1. Biol. a submicroscopic structural unit composed of a group of molecules, as in living protoplasm, starch grains, etc.
2. Chem. a structural unit, as
   1. a colloidal ion composed of an oriented arrangement of molecules
   2. an aggregate of polymerized molecules joined together

Etymology: ModL micella, dim. < L mica, a grain, crumb: see mica