Whenever I type "timeline," without a space, it gets red squiggly line. But when I search to Google, the word actually exists. Is there any difference? And please give some other compound words that can be written in many ways? Adding a dash and a space and without any.
Timeline means the linear portrayal of chronological events.
Time line is incorrect in this context (although I suppose the words could show up in some other sentence with an unrelated meaning, e.g., "the runner crossed the time line").
in to and
into are commonly confused as well, since the word
in is used last in so many two-word idiomatic phrases. Explanation: http://writingexplained.org/into-vs-in-to-difference