opuštati

1. (with se) to relax; to unwind
   Vikendom se opuštam uz knjigu i kafu. — At weekends I unwind with a book and a coffee.
   Posle posla se opušta uz muziku. — After work he relaxes to music.
2. (+ acc.) to relax; to loosen
   Ova vežba opušta mišiće leđa. — This exercise relaxes the back muscles.
   Posle ručka uvek opušta kaiš. — After lunch he always loosens his belt.

The perfective is opustiti (se).