Halloo (verb)

1. To shout out in order to attract attention or signal to someone.
2. To make a loud cry, especially to summon someone or to encourage someone to do something.

Origin:

A variant of the word "holla", which is of imitative origin, or the old english word "hal", meaning "to call ou.t"

Examples:

1. He hallooed to his friends from the other side of the street.
2. The hunters hallooed to each other to coordinate their search.
3. The coach hallooed to his team to encourage them during the game.
4. She hallooed to the children to come inside for dinner.
5. The crowd hallooed as the band came out on stage.