fellow vs lad

fellow and lad both are nouns.

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

As nouns, fellow and lad are synonyms defined as:

Other synonyms of fellow include blighter, bloke, chap, cuss, fella, feller, gent.

fellow (noun)	lad (noun)
a boy or man	a male child (a familiar term of address to a boy)
a man who is the lover of a man or woman	a boy or man
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