1) A light-sensitive neuroendocrine organ attached to the roof of the third ventricle of the brain. The pineal gland secretes melatonin, other biogenic amines, and neuropeptides.

2) A small body that arises from the roof of the third ventricle and is enclosed by the pia mater and that functions primarily as an endocrine gland that produces melatonin -- called also pineal, pineal body, pineal organ.

3) A tiny organ in the cerebrum that produces melatonin.