Here’s a set of words that have been an ongoing problem among writers.
Long-term with a hyphen, as in long-term disability, is the correct form.
The confusion probably comes from the fact that a similar adjective, longtime, is now widely accepted in dictionaries and stylebooks as hyphenless. That isn’t the case with long-term, though, at least in the short-term.
And, of course, long term as two words always is incorrect. A compound word used as an adjective, a hyphen is needed.
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