to find out definitely; learn with certainty or assurance; determine: to ascertain the facts.
2.
Archaic. to make certain, clear, or definitely known.
Origin: 1400–50; late Middle English, variant of assertain, acertain < Middle French acertain- (tonic stem of acertener to make certain), equivalent to a-a-5 + certaincertain
a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.
an extraordinary or unusual thing, person, or event; an exceptional example or instance.
a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.
a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.
early 15c., "to inform, to give assurance," from O.Fr. acertener "to assure" (13c.), from a "to" + certain "certain" (see certain). Modern meaning of "to find out for sure by experiment or investigation" is first attested 1794.