Nouns

(n)bellow, bellowing, holla, holler, hollering, hollo, holloa, roar, roaring, yowla very loud utterance (like the sound of an animal)“his bellow filled the hallway”

Verbs

(v)holloencourage somebody by crying ‘hollo’
(v)hollocry ‘hollo’
(v)shout, shout out, cry, call, yell, scream, holler, hollo, squallutter a sudden loud cry“she cried with pain when the doctor inserted the needle”, “I yelled to her from the window but she couldn't hear me”