forehead vs brow

forehead and brow both are nouns.

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

As nouns, forehead and brow are synonyms defined as:

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