irrefragable (adj.)

"that cannot be refuted," literally "incapable of being broken down," 1530s, from French irréfragable (16c.) and directly from Late Latin irrefragabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + Latin refragari "to oppose, contest," from re- "back" (see re-) + frag-, base of frangere "to break" (from PIE root *bhreg- "to break"). Related: irrefragably; irrefragability.