Толковый словарь английского языка Oxford English Reference - halloo

int., n., & v. --int. 1 inciting dogs to the chase. 2 calling attention. 3 expressing surprise. --n. the cry 'halloo'. --v. (halloos, hallooed) 1 intr. cry 'halloo', esp. to dogs. 2 intr. shout to attract attention. 3 tr. urge on (dogs etc.) with shouts. Etymology: perh. f. hallow pursue with shouts f. OF halloer (imit.)