The quality or state of being forbidding; the degree to which something seems threatening or discourages approach.
From 'forbidding' (adjective) + '-ness' (noun suffix forming abstract qualities). Built on the same Old English 'forbeodan' root as 'forbid,' with the abstract noun ending '-ness' added to create a noun around 1600.
This word is rarely used today, but it's exactly what poets and old writers needed to describe that inexplicable feeling when a place or person makes you instinctively want to retreat—it's the noun form of an emotional warning sign.
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