bench mark vs benchmark

bench mark and benchmark both are nouns.

Word	Noun	Adjective	Verb	Adverb
bench mark	Yes	No	No	No
benchmark	Yes	No	No	No

As nouns, bench mark and benchmark are synonyms defined as:

bench mark and benchmark: a surveyor's mark on a permanent object of predetermined position and elevation used as a reference point

bench mark (noun)	benchmark (noun)
a surveyor's mark on a permanent object of predetermined position and elevation used as a reference point	a standard by which something can be measured or judged
	a surveyor's mark on a permanent object of predetermined position and elevation used as a reference point