jews' harp vs jew's harp

jews' harp and jew's harp both are nouns.

Word	Noun	Adjective	Verb	Adverb
jews' harp	Yes	No	No	No
jew's harp	Yes	No	No	No

As nouns, jews' harp and jew's harp are synonyms defined as:

jews' harp and jew's harp: a small lyre-shaped musical instrument that is placed between the teeth and played by twanging a wire tongue while changing the shape of the mouth cavity

Other synonyms of jews' harp include mouth bow.

jews' harp (noun)	jew's harp (noun)
a small lyre-shaped musical instrument that is placed between the teeth and played by twanging a wire tongue while changing the shape of the mouth cavity	a small lyre-shaped musical instrument that is placed between the teeth and played by twanging a wire tongue while changing the shape of the mouth cavity