"Each of a number of flattened sacs inside a chloroplast, bounded by pigmented membranes on which the light reactions of photosynthesis take place, and arranged in stacks or grana", 1960s: from German Thylakoid, from Greek thulakoidēs 'pouch-like', from thulakos 'pouch'.[thylakoid etymology, thylakoid origin, 英语词源]