Just got through watching “Midnight Mary” on TCM starring a young Loretta Young, and noticed something I have seen in old movies a couple of times before- “to-day” instead of “today” in ads, as in “no jobs to-day”. Why was this done? Was it common? Why/when did it fall out of favor?
Very common. The general evolution of the word was from “to day” to “to-day” to “today.” The OED doesn’t have exact dates, but by the 19th century “to-day” seems to be the common form, with “today” taking over in the 20th (there are also some exceptions – the path wasn’t smooth).
The English language has a general tendency to shorten phrases and then to place their component parts next to one another. Connecting them with a hyphen follows, and time and familiarity gradually erodes the hyphen. Modern usage is similar but faster. E.g., electronic mail - e-mail - email.
Today is really a compound word, shortening the expression to the day.
The Online Etymology Dictionary says of today:
Tomorrow is quite similar:
Some 19th century prose looks today as if it were composed by a drunken computer typesetting system, Take this line from Twain’s intro to Huck Finn:
The use of the hyphen remained standard in formal English later than the early 20th century, as later quotes even for to-day and to-morrow are easy to find. Probably it wasn’t until after WWII that standards relaxed and the removal of hyphens became the norm.
I am a great believer in trying to preserve what is proper and correct English usage. At the same time, I strongly favor saving keystrokes, so long ago I went from “e-mail” to “email,” etc.
Oddly, on those rare occasions when I write on, what do you call it, oh yeah, paper, with a pen, I tend to avoid the shortcuts. See what computers have done to us? 
I’m a good Canadian, so I try to avoid dropping the hyphen in “e-mail” to preclude confusion with “enamel.”
Unless, of course, you spell it “e-namel.”
That should be namel, eh? 
I find myself instinctively typing “e-mail”, backspacing to remove the hyphen. I’ve used email since 1987, back in the days when it was really called “electronic mail,” so I’m more familiar with the hyphenated name.
I still find myself using “the Web” or “the WWW” instead of “the web” - the lowercase “web” seems to be the norm now.
Anyghow, back on topic. I’ve seen lots of old references to “base-ball”, but not “foot-ball” or “basket-ball.” Were the hyphens ever used in what is now called “football” and “basketball?” What about terms that really didn’t come into usage after WWII, like “freeway” and “expressway” - were they ever “free-way” and “express-way?”
Earlier thread on the same subject, complete with statistics from samclem.
Poet William Stafford often hyphenated the word. I wasked him why. He said the word was once meant to be visual: to-day, meaning “everything to this day,” not “on this day” was many believe.
When I was in college in 1972 there had old cast iron signs that were pounded into the ground to direct voters to the polls on election day. Those signs were from the interwar period, as the college was founded circa 1917. They spelled it “to-day”.
That is the only time I have seen it spelled like that, but then I have not traveled much, either.
I read a lot of books from the 19th century and earlier and have seen it hundreds of times.
In the late 1920s, an English publisher commissioned a 100+ series of short books from experts on what the future would look like. They called it “To-Day and To-Morrow.” An American publisher reprinted them with the same spelling.
What would startle modern audiences far, far more than the hyphens was that the actual title of almost every book was a Greek or Roman name whose association with the field being talked about would be obvious to any educated student of the day, since all British schools mandated Greek and Latin courses.
A sampling from the middle.
• Thamyris, or Is There a Future for Poetry? by R. C. Trevelyan
• Proteus, or the Future of Intelligence by Vernon Lee
• Timotheus, the Future of the Theatre by Bonamy Dobrée
A quick newspaper search finds “to-day and to-morrow” in use in British and Canadian papers through the end of the century.
According to Google’s Ngram (N-gram?) viewer, “today” first surpassed “to-day” in 1917. There is a long tail extending beyond 1965 for the hyphenated version. Of course some instances of that Ngram might not be used with the same meaning. For example, they could be part of something else like “day-to-day”.
I searched on “to-day and to-tomorrow” to get around that problem. Even so, some of the newspaper uses were mentions of old poems rather than new usages. Ngrams is a great tool, but you have to go into the texts to make sure that the hits are the usages you want.
When I put to-day and to-tomorrow into ngrams, I also saw a diminishing use the closer the time was. By the 21st century every hit was an old quote except for one book on the To-day and To-morrow series.
Teen-ager is another word nobody remembers used to be hyphenated.
On the flip side, Spider-man has always had the hyphen, but ngrams says the vast majority left it out until the 21st century.
I note we’ve left this dormant 20 years and just to-day picked it right back up where we left off. Which is a wonderful thing; no complaints from me.
Although I do question @Nick1949’s (Hi & welcome!) contention that to-day meant “History up to the current day” rather than “This current day”. Does anyone have cites one way or another?
Same here. Looking at Project Gutenberg’s html version of “Vanity Fair” (for instance) shows 21 instances of “to-day” and 1 instance of “today” (a typo?). Likewise, 40 instances of “to-morrow” and 2 instances of “tomorrow”.
That’s also my main source of classic literature, and I think they mostly use to digitize their books from early editions, with the original spelling intact.
Etymonline.com has this to say:
Middle English to dai “on this day,” from Old English todæge, to dæge “on (this present) 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, “this day; any day considered as present.” Generally it was written as two words until 16c., after which it usually was written to-day until early 20c.
I’m seeing nothing that says it was ever “up to the current day.”
I think that’s the case, with the caveat that optical character recognition errors are (sometimes?) fixed by hand. So a modern Gutenberg volunteer could have put in “today” instead of “to-day” in a case where the OCR was ambiguous.
I’m pretty sure I remember seeing at least one instance of a word in a Project Gutenberg book that was extremely unlikely to have been in the original, but I don’t remember the specifics.