silly vs youngster

silly and youngster both are nouns.

Word	Noun	Adjective	Verb	Adverb
silly	Yes	Yes	No	No
youngster	Yes	No	No	No

As nouns, youngster is a hypernym of silly; that is, youngster is a word with a broader meaning than silly:

Other hypernyms of silly include child, fry, kid, minor, nestling, nipper, shaver, small fry, tiddler, tike, tyke.

silly (noun)	youngster (noun)
a word used for misbehaving children	a young person of either sex

silly (adjective)	youngster (adjective)
dazed from or as if from repeated blows
ludicrous, foolish
lacking seriousness; given to frivolity
inspiring scornful pity