solar day vs tomorrow

solar day and tomorrow both are nouns.

Word	Noun	Adjective	Verb	Adverb
solar day	Yes	No	No	No
tomorrow	Yes	No	No	Yes

As nouns, tomorrow is a hyponym of solar day; that is, tomorrow is a word with a more specific, narrower meaning than solar day:

Other hyponyms of solar day include today, yesterday, morrow, eve, date, day of the month, date, snow day.

solar day (noun)	tomorrow (noun)
time for Earth to make a complete rotation on its axis	the near future
	the day after today

solar day (adverb)	tomorrow (adverb)
	the next day, the day after, following the present day