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Wiktionary Word definitions in Wiktionary
a. clearly true; providing no possibility of doubt. n. That which is indubitable.

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
mid-15c., from Latin indubitabilis "that cannot be doubted," from in- "not, opposite of" (see in- (1)) + dubitabilis "doubtful," from dubitare "hesitate, doubt" (see doubt ).

WordNet Word definitions in WordNet
adj. too obvious to be doubted [syn: beyond doubt(p) ]

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Indubitable \In*du"bi*ta*ble\, a. [L. indubitabilis: cf. F. indubitable. See In- not, and Dubitable .] Not dubitable or doubtful; too evident to admit of doubt; unquestionable; evident; apparently certain; as, an indubitable conclusion. -- n. That which ...