thylakoid
noun
thy·la·koid ˈthī-lə-ˌkȯid 
: any of the membranous disks of lamellae within plant chloroplasts that are composed of protein and lipid and are the sites of the photochemical reactions of photosynthesis
Example Sentences
Recent Examples on the Web Spinach is a source of thylakoids, the chlorophyll-bearing parts of green leaves. 
Lisa Drayer, CNN, 8 Mar. 2018
Lisa Drayer, CNN, 8 Mar. 2018 Word History
Etymology
International Scientific Vocabulary thylak- (from Greek thylakos sack) + -oid
First Known Use
1962, in the meaning defined above