nowadays vs today

nowadays and today both are nouns.

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

As nouns, today is a hyponym of nowadays; that is, today 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
today: the present time or age

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

As adverbs, nowadays and today are synonyms defined as:

Other synonyms of nowadays include now.

nowadays (noun)	today (noun)
the period of time that is happening now; any continuous stretch of time including the moment of speech	the present time or age
	the day that includes the present moment (as opposed to yesterday or tomorrow)

nowadays (adverb)	today (adverb)
in these times	on this day as distinct from yesterday or tomorrow
	in these times