singleton vs I

singleton and I both are nouns.

Word	Noun	Adjective	Verb	Adverb
singleton	Yes	No	No	No
I	Yes	No	No	No

As nouns, I is a hypernym of singleton; that is, I is a word with a broader meaning than singleton:

Other hypernyms of singleton include 1, ace, one, single, unity.

singleton (noun)	I (noun)
the playing card that is the only card in a suit held in a bridge hand as initially dealt	the 9th letter of the Roman alphabet
a set containing a single member	the smallest whole number or a numeral representing this number
a single object (as distinguished from a pair)	a nonmetallic element belonging to the halogens; used especially in medicine and photography and in dyes; occurs naturally only in combination in small quantities (as in sea water or rocks)