Possible meanings:
* If it's a misspelling: It could be meant to be "unveil," which means to reveal something that was hidden or secret.
* If it's a made-up word: It could be a creative expression that means something specific to a particular context, such as:
* To reverse the action of hailing: If you hailed a taxi, "unhailing" could mean to cancel the request.
* To remove something from a hail: If you were caught in a hailstorm, "unhailing" could mean to remove hailstones from something.
To understand the intended meaning, you need more context:
* What sentence was the word used in?
* What is the overall topic of the text?
Without more information, it's impossible to determine the intended meaning of "unhail."