Etymology
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indubitable (adj.)
mid-15c., "too plain to admit of doubt," from Latin indubitabilis "that cannot be doubted," from in- "not, opposite of" (see in- (1)) + dubitabilis "doubtful," from dubitare "hesitate, doubt" (see doubt (v.)).
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indubitably (adv.)
"unquestionably, without a doubt," late 15c., from indubitable + -ly (2).
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