Woe comes from Old English wā, wǣ, originally an exclamation of grief, of imitative/interjectional origin, common to many Indo-European languages (compare Latin vae, German weh). In current use it is a noun and intj meaning "great sorrow or distress, or a cause of such grief". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The history is mainly one of transmission into English, with the older form and sense carried through borrowing or adaptation. A central historical form is Old English wā. Related English forms include woeful. Derived forms include woeful and woebegone. For dictionary purposes, the important point is the continuity between the older form, the route into English, and the present lexical sense.