Definition of acid adjective from the Oxford Advanced American Dictionary
acid
adjective
/ˈæsɪd/
1(technical)that contains acid or has the essential characteristics of an acid; that has a pH of less than sevenRye can grow in acid soil. compare alkaline2that has a bitter, sharp tastesynonymsouracid fruit3 (of a person's remarks) critical and unkindsynonymcuttingsynonymsarcastican acid wit