indeclinable

詳細解釋：

in.de.clin.a.ble

adj.（形容詞）
Without grammatical inflection.
無語法形態變化的
Of, relating to, or being a word that lacks grammatical inflection though belonging to a form class whose members are usually inflected.
無詞形變化的：無語法形態變化的詞或與其有關的，儘管通常該詞所屬類型的其他詞都要發生語法形態的變化