Old English widewe, widuwe, from Proto-Germanic *widewo (cf. Old Saxon widowa, Old Frisian widwe, Middle Dutch, Dutch weduwe, Dutch weeuw, Old High German wituwa, German Witwe, Gothic widuwo), from PIE adj. *widhewo (cf. Sanskrit vidhuh "lonely, solitary," vidhava "widow;" Avestan vithava, Latin vidua, Old Church Slavonic vidova, Russian vdova, Old Irish fedb, Welsh guedeu "widow;" Persian beva, Greek eitheos "unmarried man;" Latin viduus "bereft, void"), from root *weidh- "to separate" (cf. second element in Latin di-videre "to divide;" see with).
As a prefix to a name, attested from 1570s. Meaning "short line of type" (especially at the top of a column) is 1904 print shop slang. Widow's mite is from Mark xii:43. Widow's peak is from the belief that hair growing to a point on the forehead is an omen of early widowhood, suggestive of the "peak" of a widow's hood. Widow maker "anything lethally dangerous" first recorded 1945, originally among loggers, in reference to dead trees, etc. The widow bird (1747) so-called in reference to the long black tail feathers of the males, suggestive of widows' veils.