nagao

1. sudden; abrupt; sharp
   Došlo je do naglog pada temperature. — There was a sudden drop in temperature.
   Nagla promena vremena mi ne prija. — The abrupt change in the weather doesn't agree with me.
2. hasty; rash
   Nemoj donositi nagle odluke. — Don't make hasty decisions.
   Bio sam previše nagao, izvini. — I was too rash, sorry.
3. (of a person, temper) hot-tempered; quick-tempered
   Njen otac je čovek nagle naravi. — Her father is a hot-tempered man.

The adverb naglo "suddenly; sharply" is very common: naglo je zakočio.