ustrajati

1. Croat. (+ u + loc.) to persist; to persevere
   On je ustrajao u svojoj odluci uprkos pritiscima. — He persisted in his decision despite the pressure.
   Ako ustrajete, rezultati će sigurno doći. — If you persevere, the results will surely come.

In Serbia: istrajati (pf.) / istrajavati (impf.); ustrajati is the Croatian form, though it occasionally occurs in Serbian texts too.