tur

1. colloq. bottom; backside
   Pao je na tur i svi su se smejali. — He fell on his bottom and everyone laughed.
2. (of clothing) seat of the trousers
   Pocepao je pantalone na turu dok se penjao na ogradu. — He tore the seat of his trousers climbing the fence.
3. aurochs
   Poslednji tur uginuo je u Poljskoj 1627. godine. — The last aurochs died in Poland in 1627.

In the sense "bottom" the word is colloquial but not rude; in everyday speech guza (a mild colloquial word) or dupe (coarse, vulgar) are more frequent.