indeclinable

in.de.clin.a.ble

adj.（形容词）
Without grammatical inflection.
无语法形态变化的
Of, relating to, or being a word that lacks grammatical inflection though belonging to a form class whose members are usually inflected.
无词形变化的：无语法形态变化的词或与其有关的，尽管通常该词所属类型的其他词都要发生语法形态的变化