Anti is a prefix that has several meanings: opposition and prevention against, are two of them. In the case of anti-conceptivo, it is prevention of conception; before refers to an action that takes place prior to another: " I wash my hands before eating ". That is why the phrase the contraceptive may not mean the same as the phrase before.
* Only one "like" per meaning and day, the more "likes" the meaning will appear higher in the list
