singleton vs fellow

singleton and fellow both are nouns.

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

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

Other hyponyms of singleton include mate.

singleton (noun)	fellow (noun)
the playing card that is the only card in a suit held in a bridge hand as initially dealt	a boy or man
a set containing a single member	a man who is the lover of a man or woman
a single object (as distinguished from a pair)	a friend who is frequently in the company of another
	a person who is member of one's class or profession
	an informal form of address for a man
	a member of a learned society
	one of a pair