I vs singleton

I and singleton both are nouns.

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

As nouns, singleton is a hyponym of I; that is, singleton is a word with a more specific, narrower meaning than I:

Other hyponyms of I include monad, monas.

I (noun)	singleton (noun)
the 9th letter of the Roman alphabet	the playing card that is the only card in a suit held in a bridge hand as initially dealt
the smallest whole number or a numeral representing this number	a set containing a single member
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)	a single object (as distinguished from a pair)