From Middle English tart, from Old English teart ("sharp, rough, severe"), from Proto-Germanic *tartaz ("rough, sharp, tearing"), from Proto-Germanic *teraną ("to tear"), from Proto-Indo-European *der- ("to flay, split, cleave"). Related to Dutch tarten ("to defy, challenge, mock"), German trotzen ("to defy, brave, mock"), German zart ("delicate, tender"), perhaps Albanian thartë ("sour, acid, sharp").
From Middle English tart, tarte, from Old French tarte, tartre (compare Medieval Latin tarta), of unknown origin. Perhaps an alteration of Old French torte, tourte, from Vulgar Latin *torta, from torta panis, from feminine of Latin tortus. Cognate to torta.