holloa

from WordNet (r) 3.0 (2006)

holloa
    n 1: a very loud utterance (like the sound of an animal); "his
         bellow filled the hallway" [syn: {bellow}, {bellowing},
         {holla}, {holler}, {hollering}, {hollo}, {holloa}, {roar},
         {roaring}, {yowl}]

from The Collaborative International Dictionary of English v.0.48

Holloa \Hol*loa"\, interj., n. & v. i.
   Same as {Hollo}.
   [1913 Webster]