Insidious 是個形容詞，意為「潛伏的；暗中為害的」，如 High blood pressure is an insidious condition which has few symptoms. (高血壓是一種沒什麼症狀的潛伏性疾病)。這個字衍生自拉丁字 insidiosus，後者意為「狡猾的，奸詐的」。Insidious 的副詞和名詞分別為 insidiously 和 insidiousness。
Invidious 也是形容詞，意為「易引起反感的；(尤指由於不公平) 可能招致不滿的」，如 He was in the invidious position of having to sack her. (他不得不解僱她，這引起反感)。這個字亦意為「厚此薄彼的」，如 Such choices/decisions are invidious. (這樣的選擇/決策是不公平的)。這個字衍生自拉丁字 invidiosus，後者意為「忌妒的」。Invidious 的副詞和名詞分別為 invidiously 和 invidiousness。