In a manner that is able to be confused or can easily be mistaken for something else.
From confusable + -ly (manner adverb). The -ly suffix comes from Old English -lice, originally meaning 'in the manner of,' attaching to adjectives to form adverbs.
This adverb is rarely used because English speakers usually prefer saying 'in a confusing way' or 'confusingly' instead, showing how some grammatically valid words don't actually survive in real conversation.
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