nightstick vs billy

nightstick and billy both are nouns.

Word	Noun	Adjective	Verb	Adverb
nightstick	Yes	No	No	No
billy	Yes	No	No	No

As nouns, nightstick and billy are synonyms defined as:

Other synonyms of nightstick include baton, billy club, billystick, truncheon.

nightstick (noun)	billy (noun)
a short stout club used primarily by policemen	male goat
	a short stout club used primarily by policemen