Noah Webster
Halloo
HAL'LOO, verb intransitive To cry out; to exclaim with a loud voice; to call to by name, or by the word halloo
Country folks hallooed and hooted after me.
HAL'LOO, verb transitive To encourage with shouts.
Old John hallooes his hounds again.
1. To chase with shouts.
2. To call or shout to.
[This verb is regular, and pronounced with the accent on the first syllable.]
HALLOO', an exclamation, used as a call to invite attention.