felsicPronunciation: /ˈfɛlsɪk/Definition of felsic adjective Geology relating to or denoting a group of light-coloured minerals including feldspar, feldspathoids, quartz, and muscovite: felsic volcanic rocksOften contrasted with mafic.Origin: early 20th century: from feldspar + a contraction of silicafelsic in other Oxford dictionaries Definition of felsic in the US English dictionary