The distant part of the sea visible from the shore, or slang for something that is about to happen soon.
From 'off' plus '-ing.' In nautical terminology, 'the offing' referred to the far horizon where ships disappeared. The 'about to happen' meaning emerged in 20th-century slang.
When sailors saw a ship disappear over the horizon 'in the offing,' they couldn't see it anymore—so 'in the offing' came to mean something you can't quite see yet, like the future!
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