pathway vs commissure

pathway and commissure both are nouns.

Word	Noun	Adjective	Verb	Adverb
pathway	Yes	No	No	No
commissure	Yes	No	No	No

As nouns, commissure is a hyponym of pathway; that is, commissure is a word with a more specific, narrower meaning than pathway:

pathway: a bundle of myelinated nerve fibers following a path through the brain
commissure: a bundle of nerve fibers passing from one side to the other of the brain or spinal cord

Other hyponyms of pathway include optic radiation, radiatio optica, cerebral peduncle, peduncle.

pathway (noun)	commissure (noun)
a trodden path	a bundle of nerve fibers passing from one side to the other of the brain or spinal cord
a bundle of myelinated nerve fibers following a path through the brain