Plural of choroid; the dark, vascular layer of the eye that lies between the retina and sclera, supplying blood to the retina.
From Greek khoreoeides 'vein-like' (khore 'string' + eidos 'form') + plural -s. Named for its vein-like appearance under ancient microscopy.
The choroid's dark color is why the back of your eye appears black in photos—those blood vessels absorb light so your retina can focus clearly without reflections.
Complete word intelligence in one call. Free tier — 50 lookups/day.