Widow dates back to Old English. The OED2’s earliest citation is from before 825 in the Vespasian Psalter:
Sien bearn his asteapte & wif his widwe.
(Orphaned is his son & his wife a widow.)
The verb form appears in the Middle English period. From the 14th century Northumbrian poem Cursor Mundi:
Ik am nu widuit of mi spus.
(I am now widowed of my spouse.)
The Old English widewe is cognate with many words in various Indo-European languages. The Indo-European root *widh means to separate, to be empty. This root is also, via Latin, the source of the word divide. Cognates meaning widow are the Latin Vidua, French veuve, Italian vedova, Spanish viuda, the Russian and Czech vdova, the Welsh gweddr, the German witwe, the Dutch weduwe, and the Sanskrit vidhavā.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2015, by David Wilton