šaptati

1. to whisper
   Deca su šaptala da ne probude bebu. — The children were whispering so as not to wake the baby.
   Šapće mi nešto na uvo, ali ne razumem. — He's whispering something in my ear, but I can't understand.
2. (at school, in theatre) to prompt; to whisper the answer
   Nemoj da mu šapćeš, neka sam odgovori! — Don't prompt him, let him answer on his own!

In everyday speech the variant šaputati is more common.