What is the meaning of ascertain?

verb

• Establish after a calculation, investigation, experiment, survey, or study.
  • usage: "find the product of two numbers"; "The physicist who found the elusive particle won the Nobel Prize"
  • synonyms: determine, find, find out
• Be careful or certain to do something; make certain of something.
  • usage: "He verified that the valves were closed"; "See that the curtains are closed"; "control the quality of the product"
  • synonyms: see, check, insure, see to it, ensure, control, assure
• Find out, learn, or determine with certainty, usually by making an inquiry or other effort.
  • usage: "I want to see whether she speaks French"; "See whether it works"; "find out if he speaks Russian"; "Check whether the train leaves on time"
  • synonyms: determine, check, find out, see, watch, learn
• Learn or discover with certainty. .