ascerˈtainably,adv. [f. as prec. + -ly2.] In an ascertainable manner; recognizably. 1863Kinglake Crimea I. 335 His notions..of what was plausible and what was ascertainably false.1872Liddon Elem.Relig. i. 25 To despair of knowledge only when knowledge is ascertainably out of reach.