anti- Definition

1. Signifying opposed to.

Example: anti-vivisectionist march
2. Signifying designed for retaliation against or for the immobilization or destruction of.

Example: anti-aircraft fire
3. Signifying opposite to.

Example: anticlockwise
Example: anticlimax
4. Said mainly of drugs, remedies, etc: having the effect of counteracting, inhibiting, resisting, neutralizing or reversing.

Example: antidepressant
Example: antibiotic
Example: antitoxin
5. Said of a device, product, etc: preventing; having a counteracting effect.

Example: antifreeze
Example: anti-lock braking system
6. Signifying different from what might be expected, especially in being less worthy, satisfying, etc; unconventional.

Example: antihero
7. Signifying set up as a rival or alternative. Compare pro-¹.

Example: Antichrist
Example: antipope