tract vs commissure

tract and commissure both are nouns.

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

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

tract: 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 tract include optic radiation, radiatio optica, cerebral peduncle, peduncle.

tract (noun)	commissure (noun)
a bundle of myelinated nerve fibers following a path through the brain	a bundle of nerve fibers passing from one side to the other of the brain or spinal cord
a system of body parts that together serve some particular purpose
a brief treatise on a subject of interest; published in the form of a booklet
an extended area of land