/thuy"leuh koyd'/ , 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.
[ 1965-70; Thylakoid thylakoeidés resembling a bag, equiv. to thýlak ( os ) sack + -oeides -OID ]