1. (a.) Turning sour; readily becoming tart or acid; slightly sour.

2. (n.) A substance liable to become sour.

acerb acerbate acescent acetose acid acidic acidulent acidulous acrid acrimonious amaroidal asperous astringent biting bitter bitter as gall burning caustic choleric coarse corroding corrosive crab crabbed cutting dry embittered escharotic green hard harsh incisive irritating keen mordacious mordant nose-tickling penetrating pickled piercing piquant poignant pungent rancorous rankled resentful resenting rough scathing scorching sec severe sharp sore sour sour as vinegar soured sourish splenetic stabbing stewing stinging tart tartish trenchant unripe unsweet unsweetened vinegarish vinegary virulent vitriolic withering