From Middle English halou, halow, halloo (interjection used to call attention), representing Old English hēlā, ǣlā, ēalā (“O!, alas!, oh!, lo!”), equivalent to hey + lo.
From Middle English halou, halow, halloo (interjection used to call attention), representing Old English hēlā, ǣlā, ēalā (“O!, alas!, oh!, lo!”), equivalent to hey + lo.