acidic,a.Min.|əˈsɪdɪk|[f.acid + -ic.]1.Applied by Dana to that element in a ternary compound mineral, which forms an oxygen, sulphur, or other salt, with a basic element;e.g.the silicon in silicate of lime. See quotation under acidific.1880DanaMineral.Introd.16In some classes of compounds only part of the oxygen serves to unite the acidic element to the basic.2.Abounding in an acidic element, usually silicon.1877GreenPhys.Geol.ii. §5. 47So the Crystalline rocks can be divided..into the Highly Silicated or Acidic rocks.1878Lawrencetr.Cotta, Rocks Classified 120The acidic rocks..are distinguished by a felspar richer in silica.1879RutleyStudy of Rocks iv. 34Both acidic and basic rocks are known in some instances to have emanated, etc.3.Of, pertaining to, or of the nature of, an acid. Also fig.1889inCent.Dict.1905HarmsworthEncycl.II. 1162/2Though neutral to litmus, carbon disulphide exhibits some acidic properties, uniting with alkaline sulphides to form sulpho-carbonates.1961John O'London's 21 Dec. 678/3Starkly etched portraits of immigrants in New York heat⁓wave, doom-laden acidic.