[verb] [formal] - to discover; to make certainThe police have so far been unable to ascertain the cause of the explosion. [T]I ascertained that no one could overhear us before I told Otto the news. [+ that clause]Have you ascertained whether she's coming or not? [+ wh- word]
ASCERTAIN
Meaning of ASCERTAIN in English
Cambridge English vocab. Кембриджский английский словарь. 2012