There are several words in the English which have been created as a "merging" of multiple existing words.
e.g. Insofar- Merged from words "in, so, far".
How do such words come about?
It surely can't simply be a matter of a mistake growing in usage so much that it is eventually accepted as valid, because there are so many examples for which this has not happened.
e.g. "alot"- This is not a valid word, although it is commonly written.