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The expression logically should be "feats of daring-do" because that's just what it means: deeds of extreme daring. But through a chain of misunderstandings explained in the Oxford English Dictionary, the standard form evolved with the unusual spelling "derring-do," and "daring-do" is an error.
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SOL returns 45 stories containing variants of 'daring-do' and 28 stories containing variants of 'derring-do'.
AJ