Tart has this etymological history: The adjective 'sharp-tasting' is from Old English teart ('sharp, severe, rough'), of uncertain further origin. The noun 'small pastry' is a separate word from Old French tarte, of uncertain origin. The historical chain includes Old English teart. The quoted older senses, "sharp-tasting", "sharp, severe, rough", and "small pastry", supply the semantic anchors for tart. The formation is best read as borrowed: the word tart carries its older form-history into a compact English lexical shape. In present English it is used as a adj, "sharp or sour in taste; a small open pastry with filling". English derivatives include tartly and tartness. The result is a adj and noun whose etymology preserves both the older form and the later English specialization.