button hole vs buttonhole

button hole and buttonhole both are nouns.

Word	Noun	Adjective	Verb	Adverb
button hole	Yes	No	No	No
buttonhole	Yes	No	Yes	No

As nouns, button hole and buttonhole are synonyms defined as:

button hole (noun)	buttonhole (noun)
a hole through which buttons are pushed	a hole through which buttons are pushed

button hole (verb)	buttonhole (verb)
	detain in conversation by or as if by holding on to the outer garments of; as for political or economic favors