a chemical substance that reacts with acids to form a salt and gives a solution with a pH of more than seven when it is dissolved (= mixed with a liquid and becoming part of it) in water 碱compare acidTopics Physics and chemistryc2Word Originlate Middle English (denoting a saline substance derived from the ashes of various plants, including glasswort, a salt-marsh plant formerly used to make glass): from medieval Latin, from Arabic al-qalī ‘calcined ashes (of the glasswort etc.), reduced through exposure to strong heat’, from qalā ‘fry, roast’.