Hyphen

choi

Johnson  l  Don't Go Mad; Hyphens can be tricky, but they need not drive you crazy. Economist, June 10, 2017.

Quote:

" 'Today' overtook 'to-day' in frequency around 1926 in America, according to data from Google Books, and a lit later than that in Britain.

"English is a Germanic language that allows for many different kinds of compounds, including those made from two adjectives ('blue-green'), two nouns ('kitchen sink'), adjective-noun ('dark-room'), noun-adjective ('slate-blue') and so on. But which ones should be written separately, which hyphenated and which closed up ['email' as opposed to 'e-mail' preferred by The Economist].

Note:
(a)
(i) today (adv & noun; etymology: "Old English tō dæg on (this) day. Compare with tomorrow and tonight")
https://en.oxforddictionaries.com/definition/today
(ii)
(A) today (adv): "Generally written as two words [not to be confused with 'to date' in Modern English, which means 'until now'] until 16c, after which it usually was written to-day until early 20c")
www.etymonline.com/index.php?term=today
(B) tomorrow (adv)
www.etymonline.com/index.php?term=tomorrow
(C) tonight (adv)
www.etymonline.com/index.php?term=tonight

(b) The answer to quotation 2 depends usually on individual's taste and style, per The Economist.
© There is no need to read the rest.