kleknuti

1. to kneel down
   Kleknuo je i zaprosio je pred svima. — He knelt down and proposed to her in front of everyone.
   Kleknula je da veže detetu pertle. — She knelt down to tie the child's shoelaces.
2. (pred + instr.) to bow down; to submit
   Nikada neću kleknuti pred njima. — I will never bow down to them.

Kleknuti is the act of going down on one's knees; being on one's knees is klečati.