Etymology
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hullabaloo (n.)
1762, hollo-ballo (with many variant spellings) "uproar, racket, noisy commotion," chiefly in northern England and Scottish, perhaps a rhyming reduplication of hollo (see hello). Bartlett ("Dictionary of Americanisms," 1848) has it as hellabaloo "riotous noise; confusion," and says it is provincial in England.
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holler (v.)
1690s, American English, variant of hollo (1540s) "to shout," especially "to call to the hounds in hunting," which is related to hello. Compare colloquial yeller for yellow, etc. Related: Hollered; hollering.
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hallo (interj.)
shout to call attention, 1781, earlier hollo, holla (also see hello). "Such forms, being mere syllables to call attention, are freely varied for sonorous effect" [Century Dictionary]. Old English had ea la. Halow as a shipman's cry to incite effort is from mid-15c.; Halloo as a verb, "to pursue with shouts, to shout in the chase," is from late 14c. Compare also harou, cry of distress, late 13c., from French.
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hello (interj.)

greeting between persons meeting, 1848, early references are to the U.S. western frontier (where hello, the house was said to be the usual greeting upon approaching a habitation).

It is an alteration of hallo, itself an alteration of holla, hollo, a shout to attract attention, which seems to go back at least to late 14c. (compare Middle English verb halouen "to shout in the chase," hallouing). OED cites Old High German hala, hola, emphatic imperative of halon, holon "to fetch," "used especially in hailing a ferryman." Fowler in the 1920s listed halloo, hallo, halloa, halloo, hello, hillo, hilloa, holla, holler, hollo, holloa, hollow, hullo, and writes, "The multiplicity of forms is bewildering ...."

Its rise to popularity as a greeting (1880s) coincides with the spread of the telephone, where it won out as the word said in answering, over Alexander Graham Bell's suggestion, ahoy. Central telephone exchange operators were known as hello-girls (1889).

Hello, formerly an Americanism, is now nearly as common as hullo in Britain (Say who you are; do not just say 'hello' is the warning given in our telephone directories) and the Englishman cannot be expected to give up the right to say hello if he likes it better than his native hullo. [H.W. Fowler, "A Dictionary of Modern English Usage," 1926]
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