billy vs nightstick

billy and nightstick both are nouns.

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

As nouns, billy and nightstick are synonyms defined as:

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

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