a preventive against
collocation预防某种疾病的药物
The tablets are used as a preventive against malaria.
这些药片被用作预防疟疾的药物。
预防药；预防疗法
先理解核心含义，再看它在真实句子里的用法。
预防药；预防疗法
A medicine or treatment that prevents or slows the course of a disease.
The doctor prescribed a preventive to reduce the risk of infection.
医生开了一种预防药以降低感染风险。
避孕用品,尤其是避孕套
A contraceptive, especially a condom.
预防或延缓疾病发展的药物
remedy that prevents or slows the course of an illness or disease
阻碍物；负担
any obstruction that impedes or is burdensome
避孕用具或药物
an agent or device intended to prevent conception
Many travelers carry preventives like insect repellent when visiting tropical areas.
许多旅行者前往热带地区时会携带驱虫剂等预防用品。
The barrier acted as a preventive against the spread of the disease.
这个屏障起到了防止疾病传播的阻碍作用。
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预防某种疾病的药物
The tablets are used as a preventive against malaria.
这些药片被用作预防疟疾的药物。
服用预防药
Take a preventive before entering the jungle.
进入丛林前先服用预防药。
使用避孕药具
The doctor advised them to use a preventive during sex.
医生建议他们性交时使用避孕药具。
有效的预防药
A vaccine is an effective preventive against many diseases.
疫苗是预防多种疾病的有效方法。
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把 preventive 拆成 prevent（阻止）+ ive，记成“用来阻止/预防的东西”：避孕套、预防药、障碍物。
语域：mixed 常见场景：medical and public-health discussion、historical or euphemistic writing about contraception、formal or literary prose preventive 作名词时义项较多：指“预防药/预防措施”多用于医学或公共卫生语境；指“避孕药具（尤指避孕套）”比较常见于历史文本或委婉说法；指“阻碍物/负担”则偏正式书面。总体而言多用于正式或专门场合。
与 preventive /prɪˈvɛntɪv/ 真正押韵的词有 inventive /ɪnˈvɛntɪv/ 和 incentive /ɪnˈsɛntɪv/（重读音节的元音和后面的 /ntɪv/ 相同）；sensitive /ˈsɛnsɪtɪv/ 和 tentative /ˈtɛntətɪv/ 拼写上都含 -tive，但重音在第一个音节，发音并不相同。
Dictionary facts from ECDICT, WIKTIONARY.