Unsound comes from un- ('not') + sound ('healthy, whole'), from Old English gesund ('healthy, sound'), from Proto-Germanic *gasundaz. The historical chain includes Old English un-, Old English gesund, and Proto-Germanic *gasundaz. The quoted older senses, "not", "healthy, whole", and "healthy, sound", supply the semantic anchors for unsound. The formation is best read as compound and borrowed: the word unsound carries its older form-history into a compact English lexical shape. In present English it is used as a adj, "not in good condition; not based on valid reasoning". English derivatives include unsoundly and unsoundness; related English forms include sound and soundness. The result is a adj whose etymology preserves both the older form and the later English specialization.