- 1
Deleterious means damaging or harmful. It is a formal, often scientific or official word, not a word you throw into chat. Writers like it in front of effect, impact, or influence: a deleterious effect on health, a deleterious impact on the soil. It can name slow harm as well as a sudden blow — something that quietly spoils a body, a habit, or a system. Ordinary English would just say harmful or bad for you; deleterious tells you the speaker is being careful and a little technical. It does not mean “able to be deleted.”
有害的、有不良影響的（書面／學術）
組成Adapted from New Latin dēlētērius / dēlētōrius + English -ous, from Ancient Greek dēlētḗrios (“noxious, harmful”), from dēlētḗr (“a destroyer”), from the verb dēléomai (“I hurt, damage, spoil”). Not from delete.
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
deleteriousadj/ˌdɛl.ɪˈtɪə̯.ɹi.əs/
- 1
formalHarmful, often in a subtle or unexpected way.
- deleterious effects
- deleterious to someone's health
- 2
biologygeneticsmedicineHaving lower fitness.
- A deleterious mutation
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。