brain / head / chief, principal

(anatomy) the brain / (by extension, figuratively) one's brains, one's mental functioning

(archaic, anatomy) the brain / (archaic, by extension) the head

brain; brains / mind; intellect; understanding

(cytology) brain cell / (colloquial) neuron

(neuroanatomy) midbrain

(neurology, pathology) a stroke; a cerebrovascular accident; a cerebrovascular insult

brain cancer

gyrus (a ridge or fold on the cerebral cortex)

intracerebral; intracranial; the inside of the head / (figuratively) the inside of one's mind; within one's mind; mental (of imagined things, etc.)