early 15c., "to inform, to give assurance," from Anglo-French acerteiner, Old French acertener "to assure, certify" (13c.), from a "to" (see ad-) + certain "certain" (see certain). Modern meaning of "find out for sure by experiment or investigation" is first attested 1794. Related: Ascertained; ascertaining.
1. It can be difficult to ascertain the facts.
2. I'm going to ascertain the truth.
3. It's difficult to ascertain the coal deposits.
4. The police determined to ascertain the truth of the matter.
5. Take time to ascertain what services your bank is providing, and at what cost.