Hello is defined as a greeting or a response when on the phone, used to bring attention or an expression of surprise.(interjection)
See hello in Webster's New World College Dictionary
Origin: var. of hollo
noun pl. hellos
See hello in American Heritage Dictionary 4
Origin: Alteration of hallo
Origin: , alteration of obsolete holla, stop!
Origin: , perhaps from Old French hola
Origin: : ho, ho!
Origin: + la, there (from Latin illāc, that way).
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