indeclinable
/ˌɪndɪˈklaɪnəbl/adjective
- Grammar (of a noun, pronoun, or adjective in a highly inflected language) having no inflections【语法】（名词, 代词, 形容词）不变格的; 无词形变化的。
词源
late Middle English: via French from Latin indeclinabilis, from in- 'not' + declinabilis 'able to be inflected' （see DECLINE）.