ascertain

verb5

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

   • As soon as we ascertain what the situation is, we can plan how to proceed.
2. •
   (old-fashioned) To look for something lost.
3. •
   (no longer used) To establish, to prove.

   • In 1695 he [Walter Moyle] was chosen to represent the borough of Saltash in parliament ; a circumstance which ascertains the piece before us to have been written subsequent to that period. — 1800
4. •
   (no longer used) To ensure or effect.

   • The ministry, in order to ascertain a majority in the house of lords, persuaded the queen to take a measure which nothing but necessity could justify. — 1757
5. •
   (no longer used) To make (someone) certain or confident about something; to inform.

   • We would most gladly ye came yourself if that ye may […] praying you to ascertain us of your News. — 1844