Pronunciation: (thī'lu-koid"), [key]
—n. Cell Biol.
a flattened sac or vesicle lined with a pigmented membrane that is the site of photosynthesis, in plants and algae occurring in interconnected stacks constituting a granum of the chloroplast, and in other photosynthesizing organisms occurring either singly or as part of the cell membrane or other structure.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.