Halloo

Definition:

(n.) A loud exclamation; a call to invite attention or to incite a person or an animal; a shout.
(v. i.) To cry out; to exclaim with a loud voice; to call to a person, as by the word halloo.
(v. t.) To encourage with shouts.
(v. t.) To chase with shouts or outcries.
(v. t.) To call or shout to; to hail.
(n.) An exclamation to call attention or to encourage one.

Compare halloo with other words:

halloo vs. hallow