Yellow; the corpus luteum.
[Latin luteus, yellow, or luteum, yolk of egg.]
The first sense is comparatively rare. It can apply to various shades of orange or yellow—something luteous can be a deep orange-yellow or a greenish yellow colour; lutescent refers to something yellowish in colour.
The corpus luteum (Latin, literally ‘yellow body’) is a hormone-secreting structure that develops in an ovary after a egg has been discharged; the process of formation is luteinization; ovulation is stimulated by luteinizing hormone; lutein is a deep yellow pigment found in the corpus luteum, among other places; the adjective luteal relates to the corpus luteum.