It's not in that particular dictionary, but you don't seem to understand Latin. Latin words are made up of roots and suffixes, the suffix changing such things as the tense or subject. It does not effect the basic meaning of the word.
All you had to do was go to the same site and look for vacante instead of empty (click on Whitaker's Words first to be able to input Latin).
Marijuana is not intrinsically evil, but too much of it is a sin.