ascerˈtaining,vbl.n. [f. as prec. + -ing1.] † Assurance, confirmation (obs.). (Now gerundial: see ascertain v. 5.) 1685Baxter Paraphr.N.T. Acts i. 9 The sight of Christ's Ascension must needs be..an ascertaining of the Apostles Faith.1835Macready Remin. I. 472 On ascertaining the time.