WordWeb Online

1. Establish after a calculation, investigation, experiment, survey, or study
   "ascertain the product of two numbers";
   - determine, find, find out
    
2. Be careful or certain to do something; make certain of something
   - see, check, insure, see to it, ensure, control, assure
    
3. Find out, learn, or determine with certainty, usually by making an inquiry or other effort
   "ascertain whether the train leaves on time";
   - determine, check, find out, see, watch, learn
    
4. Learn or discover with certainty

Derived forms: ascertained, ascertains, ascertaining

Type of: discover, find out, get a line, get wind, get word, hear, learn, pick up, see, verify