yoo-hoo /juː ˈhuː/ interjection informal
[Date: 1900-2000; Origin: A natural shout]
used to attract someone’s attention when they are a long way from you

[TahlilGaran] Dictionary of Contemporary English ▲

yoo hoo
interj.
■ Used as an informal call or shout to a person to attract his attention.
Louise opened the door and called "Yoo-hoo, Mother
■ are you home?" See: ALL RIGHT FOR YOU, I'M TELLING YOU, SAYS WHO or SAYS YOU, THAT'S --- FOR YOU, WHAT HAVE YOU.

[TahlilGaran] English Idioms Dictionary ▲