Definition of "hullo"

There he is, now. Bang went the front door open and shut. Harry shouted: “Hullo, you people. Down in five minutes.”

1918 August, Katherine Mansfield [pseudonym; Kathleen Mansfield Murry], “Bliss”, in Bliss and Other Stories, London: Constable & Company, published 1920, page 126

“Mr Wooster?” “Oh, hullo, Lady Wickham.” [...] “Hullo, Bobbie,” I said. “Hullo, Bertie,” she said. “Hullo, Upjohn,” I said. The correct response to this would have been “Hullo, Wooster”, but he blew up in his lines and merely made a noise like a wolf with its big toe caught in a trap. [...] But as I approached the [telephone] and unhooked the thing you unhook, I was far from being at my most nonchalant, and when I heard Upjohn are-you-there-ing at the other end my manly spirit definitely blew a fuse. For I could tell by his voice that he was in the testiest of moods. Not even when conferring with me at Malvern House, Bramley-on-Sea, on the occasion when I put sherbet in the ink, had I sensed in him a more marked stirred-up-ness. “Hullo? Hullo? Hullo? Are you there? Will you kindly answer me? This is Mr Upjohn speaking.”

1960, P[elham] G[renville] Wodehouse, “II, XV, AND XIX”, in Jeeves in the Offing, London: Herbert Jenkins

Suddenly Sydney gave an exclamation. ‘Hullo! — The front door’s closed!’

1897, Richard Marsh, The Beetle

"Hullo, there's a monkey's wedding," said my wife's niece, a girl of about twenty, born in South Africa […] She was looking out on the lawn, and it was one of those lovely April mornings with sunshine and rain alternating […]

1939, Country Life, volume 85, page 290