once in WordNet English dictionary

1. at a previous time
   "at one time he loved her"; "her erstwhile writing"; "she was a dancer once";
   once  formerly  at one time  erstwhile  erst  once  formerly  at one time  erstwhile  erst 
   
2. on one occasion
   "once I ran into her"
   once  one time  in one case  once  one time  in one case 
   
3. as soon as
   "once we are home, we can rest"
   once  once