Webster's Revised Unabridged Dictionary · 1913

Halloo

Halloo (hal*lo") , noun

[Perh. from ah + lo; compare Anglo-Saxon ealā, German halloh, French haler to set (a dog) on. Compare Hollo, interj.]

A loud exclamation; a call to invite attention or to incite a person or an animal; a shout.
List! List! I hear Some far off halloo break the silent air. — Milton

Halloo (-lod") , intransitive verb

To cry out; to exclaim with a loud voice; to call to a person, as by the word halloo.
Country folks hallooed and hooted after me. — Sir P. Sidney

Halloo , transitive verb

1.
To encourage with shouts.
Old John hallooes his hounds again. — Prior
2.
To chase with shouts or outcries.
If I fly... Halloo me like a hare. — Shakespeare
3.
To call or shout to; to hail. — Shakespeare

Halloo , interjection

[Old English halow. See Halloo, n.]

An exclamation to call attention or to encourage one. Now mostly replaced by hello.