brain stem vs brain-stem

brain stem and brain-stem both are nouns.

Word	Noun	Adjective	Verb	Adverb
brain stem	Yes	No	No	No
brain-stem	Yes	No	No	No

As nouns, brain stem and brain-stem are synonyms defined as:

brain stem and brain-stem: the part of the brain continuous with the spinal cord and comprising the medulla oblongata and pons and midbrain and parts of the hypothalamus

Other synonyms of brain stem include brainstem.

brain stem (noun)	brain-stem (noun)
the part of the brain continuous with the spinal cord and comprising the medulla oblongata and pons and midbrain and parts of the hypothalamus	the part of the brain continuous with the spinal cord and comprising the medulla oblongata and pons and midbrain and parts of the hypothalamus