pinealnoun [ C ]
/ˈpɪn.i.əl//ˈpɪn.i.əl/also pineal gland, /ˈpɪn.i.əl ˌɡlænd//ˈpɪn.i.əl ˌɡlænd/specialized anatomy an organ in the brain that produces a hormone called melatonin:
The pineal produces its hormone melatonin only during the dark.
pinealadjective
/ˈpɪn.i.əl//ˈpɪn.i.əl/specialized anatomy in or on the pineal, or relating to the pineal:
a pineal tumour
pineal dysfunction