strahovit

1. dreadful; horrible; terrible
   Na autoputu se desila strahovita nesreća. — There was a horrible accident on the motorway.
2. (of intensity) tremendous; immense
   Leto je bilo strahovito vruće. — The summer was tremendously hot.
   Vozio je strahovitom brzinom. — He was driving at tremendous speed.

The adverb strahovito often just means "extremely".