Yearday is a compound of year + day, from Old English ġēardæg, denoting an annual commemoration, especially of a death. In current use it is a noun meaning "an anniversary, especially of a death; a commemoration day". 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 surface form is compositional: its joined elements remain visible in the modern word. The historical chain includes Old English ġēar and Old English dæg. Related English forms include year, day, and yearly. The word's history is thus visible in its construction: the components remain interpretable even after the whole expression has settled into a conventional English meaning.