brow vs forehead

brow and forehead both are nouns.

Word	Noun	Adjective	Verb	Adverb
brow	Yes	No	No	No
forehead	Yes	No	No	No

As nouns, brow and forehead are synonyms defined as:

brow (noun)	forehead (noun)
the part of the face above the eyes	the part of the face above the eyes
the arch of hair above each eye	the large cranial bone forming the front part of the cranium: includes the upper part of the orbits
the peak of a hill