today (adv.)

Old English todæge, to dæge "on (this) day," from to "at, on" (see to) + dæge, dative of dæg "day" (see day). Meaning "in modern times" is from c. 1300. As a noun from 1530s. Generally written as two words until 16c., after which it usually was written to-day until early 20c.

Similar constructions exist in other Germanic languages, such as Dutch van daag "from-day," Danish and Swedish i dag "in day." German heute is from Old High German hiutu, from Proto-Germanic *hiu tagu "on (this) day," with first element from PIE pronominal stem *ki-, represented by Latin cis "on this side."

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Definitions of today from WordNet
today (n.)
the present time or age;
the world of today
today we have computers
today (n.)
the day that includes the present moment (as opposed to yesterday or tomorrow);
did you see today's newspaper?
today (adv.)
in these times; "it is solely by their language that the upper classes nowadays are distinguished"- Nancy Mitford;
today almost every home has television
Synonyms: nowadays / now
today (adv.)
on this day as distinct from yesterday or tomorrow;
I can't meet with you today