smirivati

1. (+ acc.) to calm; to soothe
   Mama smiruje bebu pesmom. — Mum is soothing the baby with a song.
   Ovaj čaj mi uvek smiruje živce. — This tea always calms my nerves.
2. (smirivati se) to calm down
   Posle svađe se polako smirivao. — After the argument he was slowly calming down.
3. (of a situation, weather) to die down; to settle
   Vetar se smiruje tek pred jutro. — The wind only dies down towards morning.
   Situacija na granici se polako smiruje. — The situation at the border is slowly settling down.

The perfective is smiriti (se).