curtsy vs bow down

curtsy is a noun but bow down is not a noun.

Word	Noun	Adjective	Verb	Adverb
curtsy	Yes	No	Yes	No
bow down	No	No	Yes	No

curtsy (noun)	bow down (noun)
bending the knees; a gesture of respect made by women

curtsy (verb)	bow down (verb)
make a curtsy; usually done only by girls and women; as a sign of respect	bend one's knee or body, or lower one's head
bend the knees in a gesture of respectful greeting	get into a prostrate position, as in submission