nowadays vs tonight

nowadays and tonight both are nouns.

Word	Noun	Adjective	Verb	Adverb
nowadays	Yes	No	No	Yes
tonight	Yes	No	No	Yes

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

nowadays: the period of time that is happening now; any continuous stretch of time including the moment of speech
tonight: the present or immediately coming night

Other hyponyms of nowadays include now, here and now, moment, present moment, date, nonce, time being, today.

nowadays (noun)	tonight (noun)
the period of time that is happening now; any continuous stretch of time including the moment of speech	the present or immediately coming night

nowadays (adverb)	tonight (adverb)
in these times	during the night of the present day