certainty  
noun uk/ˈsɜː.tən.ti/ us/ˈsɝː.tən.ti/
  (IN NO DOUBT)         
  [ C ]确定的事情;必然的事情 
something that cannot be doubted
  There are few absolute certainties in life. 世事无绝对。 
 B2 [ U ]肯定;确定;确实;确信 
the state of being completely confident or having no doubt about something
  I'm unable to answer that question with any certainty. 我不能确切地回答出那个问题。 
 - More examples
 - Somehow she knew, with deep-down certainty, that her son was still alive.
 - Each one of us faces the certainty that we are going to die.
 - I can't say I'm certain they'll win, because there are no certainties in life, but they've got an excellent chance.
 - Can you state with certainty that this is the same man you saw on that day?
 - He stood up and declared his faith with absolute certainty.
 
  (EXTREMELY LIKELY)      
C2 [ C ]必然的事;很有可能发生的事 
something that is very likely to happen
  Joan will win - that's a certainty. 琼会赢的——这是必然的。 
 [ + to infinitive ] Joan is a certainty to win. 琼一定会赢。