Wild, fierce, or untamed, like a catamount; savage or menacing (archaic).
From catamount with the adjectival suffix '-ain,' used metaphorically to describe something as fierce or dangerous as a wild mountain cat.
Shakespeare's contemporaries used 'catamountain' as an insult to describe someone wild and uncontrollable—it's a great example of how animals we find terrifying become used as metaphors for human behavior.
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