šapnuti

1. to whisper
   Šapnula mi je nešto na uvo. — She whispered something in my ear.
2. (in class, on stage) to prompt; to whisper the answer
   Drug mi je šapnuo odgovor na testu. — My friend whispered the answer to me during the test.
3. to tip off
   Neko mu je šapnuo da će biti otpuštanja. — Someone tipped him off that there would be layoffs.

The person addressed is in the dative: šapnuti nekome nešto (na uvo).