nadimak

1. nickname
   U školi su mu dali nadimak Profesor. — At school they gave him the nickname Professor.
   Svi je zovu po nadimku, a ne po imenu. — Everyone calls her by her nickname, not her name.

Common phrases are "dati kome nadimak" (to give someone a nickname) and "zvati koga po nadimku" (to call someone by a nickname).