Language is so ubiquitous in our lives that it can often be easy to think that the way it exists now is the way it has always been, but in reality that could not be farther from the truth. In the past the words today and tomorrow would have been spelled as to-day and to-morrow respectively. As recently as the early 1930s these spellings were more common than the current standard spellings.

Sources

• https://books.google.com/ngrams