1. 
[syn: bellow, bellowing, holla, holler, hollering, hollo, holloa, roar, roaring, yowl]
The Collaborative International Dictionary of English v.0.48:
Holla \Hol"la\, interj. [F. hola; ho ho + l[`a] there, fr. L.
   illac that way, there. Cf. Hollo.]
   Hollo.
   [1913 Webster]
The Collaborative International Dictionary of English v.0.48:
Holla \Hol"la\, v. i. [imp. & p. p. Hollaed; p. pr. & vb. n.
   Hollaing.]
   See Hollo, v. i.
   [1913 Webster]
WordNet (r) 3.0 (2006):
holla
    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]