dhātu ［界］ (, Pali;  kai): Realm, world, element, root, base, cause, or relics. The word dhātu is a component of various Sanskrit Buddhist terms: kāma-dhātu (world of desire), rūpa-dhātu (world of form), ārūpya-dhātu (world of formlessness), tri-sāhasra-mahā-sāhasra-loka-dhātu (major world system), buddha-dhātu (Buddha nature), dhātu-garbha (a sanctuary for enshrining ashes, or a sanctuary that houses ashes regarded as the Buddha; here dhātu means relics or ashes), dharma-dhātu (Dharma realm, which means both the phenomenal world and the world of the truth), etc.