skittle pin vs ninepin

skittle pin and ninepin both are nouns.

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

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

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

Other synonyms of skittle pin include skittle.

skittle pin (noun)	ninepin (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