Gikun word derived by applying Chinese-derived spelling 神聖 (“sacredness”), a term which decomposes into 神 (“God”) + 聖 (“holy”), to realis form of native Japanese verb きよむ (kiyomu, “to sanctify”) thus denoting sanctification as God making something holy.
神聖 (きよ)む[1](kiyo.mu, the archaic form of 清 (きよ)める, 浄 (きよ)める, kiyo.meru) → 神聖(しんせい) (shinsei)