Wiktionary
vb. (context transitive English) To cause (a moving vehicle) to stop by using an arm gesture.
Usage examples of "wave down".
Then he jumped onto the track and began his futile attempt to wave down the train.
Rohain hoped fervently that Viviana and Caitri, wherever they were, would wave down the Stormriders and be taken to safety at the Tower on eotaur-back.
It was the kind of land that would slow down a tsunami, Damien noted, wearing the great wave down as it crossed mile after mile of shallows, until by the time it hit shore proper there would be little left to devastate man's settlements.
He stared below, into the trees, was ready to ride, to move in one hard wave down into the face of the enemy, drive them out, drive them away.
Panic now gripped the refugees, descending in a human wave down to the landing.