ninepin vs skittle pin

ninepin and skittle pin both are nouns.

Word	Noun	Adjective	Verb	Adverb
ninepin	Yes	No	No	No
skittle pin	Yes	No	No	No

As nouns, ninepin and skittle pin are synonyms defined as:

ninepin and skittle pin: a bowling pin of the type used in playing ninepins or (in England) skittles

Other synonyms of ninepin include skittle.

ninepin (noun)	skittle pin (noun)
a bowling pin of the type used in playing ninepins or (in England) skittles	a bowling pin of the type used in playing ninepins or (in England) skittles