Holler

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late 17th century (as a verb): variant of the rare verb hollo ; related to halloo.

wiktionary

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American variant of holla, hallo or hollo.

Variation of hollow.

etymonline

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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.

holler (n.)

1896, from holler (v.); earlier hollar (1825). As a style of singing (originally Southern U.S.), attested by 1936.