mahnuti

1. (to someone) to wave
   Mahnula mi je s druge strane ulice. — She waved to me from across the street.
2. (+ instr.) to wave; to wag; to flap
   Pas je veselo mahnuo repom. — The dog wagged its tail happily.
   Mahnuo je rukom i otišao. — He waved his hand and left.

The person waved to is in the dative, the thing waved in the instrumental: mahnuti nekome rukom.