In a manner that can be beaten or defeated; in a way that makes something beatable.
From 'beatable' (adjective) plus '-ly' (adverbial suffix), following the standard pattern of turning adjectives into manner adverbs describing how something is done.
This is a rare word because we don't often need an adverb form of 'beatable'—it shows how English can technically create grammatically correct words that speakers rarely actually use, highlighting the difference between what's possible and what's probable.
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