as

1. (of a person) ace; top expert
   On je pravi as za kompjutere. — He's a real ace with computers.
   Na turniru su igrali svi teniski asovi. — All the tennis aces played at the tournament.
2. (in cards) ace
   Imao sam dva asa u ruci. — I had two aces in my hand.
3. (in tennis, volleyball) ace
   Đoković je u meču servirao deset asova. — Djokovic served ten aces in the match.

For the playing card, colloquial speech more often uses kec.