From Old Frisian hiōda, hiūdega. A contraction of the instrumental phrase *hiū dega (“this day”), from Proto-West Germanic *hiu dagu, from Proto-Germanic *hinō dagō (“on this day”), from *hiz (from which also hy) + *dagaz (from which dei). Cognate with Old English hēodæġ, Dutch heden, German Low German hüüt, German heute.