The Swedish word for headmaster is
rektor

Translations for headmaster and their definitions

rektor	©
1. n-c. a headmaster/headmistress; headteacher(R:Utrikes namnbok) (primary school; grundskola)
2. n-c. a headmaster/headmistress; principal (secondary school; gymnasieskola)
3. n-c. a principal; director (institutes and colleges; fackhögskola)
4. n-c. a rector, a headmaster, a schoolmaster; the leader of a school or other institute of education