a shout to attract attention; "he gave a great halloo but no one heard him"

urge on with shouts; "halloo the dogs in a hunt"

shout 'halloo', as when greeting someone or attracting attention

To chase with shouts or outcries.

To call or shout to; to hail. --Shak.

noun

call , holler , yell

verb

bawl , bellow , bluster , call , clamor , cry , holler , shout , vociferate , whoop , yawp , yell