From Middle English acerteynen, from Old French acertener, from a- ("to, towards") + certener ("make sure of"), from the adjective certain, from Latin certus.

• (British) IPA: /ˌæsəˈteɪn/
• (America) enPR: ăs'-ər-tānʹ, IPA: /ˌæsɚˈteɪn/

ascertain (ascertains, present participle ascertaining; simple past and past participle ascertained)

1. To find out definitely; to discover or establish.

   Synonyms: determine, discover, establish, find out, learn, work out

   As soon as we ascertain what the situation is, we can plan how to proceed.

   • 1904–1905, Baroness Orczy [i.e., Emma Orczy], “The Tremarn Case ↗”, in The Case of Miss Elliott, London: T[homas] Fisher Unwin, published 1905, →OCLC ↗; republished as popular edition, London: Greening & Co., 1909, OCLC 11192831 ↗, quoted in The Case of Miss Elliott (ebook no. 2000141h.html), Australia: Project Gutenberg of Australia, February 2020:

     “There the cause of death was soon ascertained ; the victim of this daring outrage had been stabbed to death from ear to ear with a long, sharp instrument, in shape like an antique stiletto, which […] was subsequently found under the cushions of the hansom. […] ”

2. (obsolete) To make (someone) certain or confident about something; to inform.
3. (archaic) To establish, to prove.
4. (archaic) To ensure or effect.

• French: constater, définir
• German: feststellen
• Italian: accertare, appurare, stabilire, constatare, riscontrare
• Portuguese: averiguar, determinar, estabelecer, apurar, constatar
• Russian: удостоверя́ться
• Spanish: averiguar, determinar, establecer, definir