Entry 2 senses · 2 variants Webster, 1913 Selenite /sĕl'-ĭn-ītˌ/ · Sel·e·nite · IPA /ˈsɛlɪnaɪt/ n. n. 01 n. A salt of selenious acid. 1. A salt of selenious acid.(Chem.) 02 n. A variety of gypsum, occuring in transparent crystals or crystalline masses. 1. A variety of gypsum, occuring in transparent crystals or crystalline masses.(Min.)