holla(n = noun.communication) bellow, bellowing, holler, hollering, hollo, holloa, roar, roaring, yowl - a very loud utterance (like the sound of an animal); "his bellow filled the hallway"
is a kind of call, cry, outcry, shout, vociferation, yell

   Hollo. [1913 Webster]

   See Hollo, v. i. [1913 Webster]

holla, int., n., & v.
--int. calling attention.
--n. a cry of 'holla'.
--v. (hollas, hollaed or holla'd, hollaing)
1 intr. shout.
2 tr. call to (hounds).

Etymology:
F hol{agrave} (as HO, l{agrave} there)