If you're thinking of the historical Renaissance:
* Dark Ages: This is the period preceding the Renaissance, often characterized as a time of decline in learning and culture.
* Medieval Period: While not directly antagonistic, this period represents the time before the Renaissance.
* Decline: This could be used to describe a period of cultural, artistic, or intellectual stagnation after a flourishing period.
If you're thinking of the broader meaning of rebirth or revival:
* Decline: This refers to a general downward trend, the opposite of a revival.
* Stagnation: This refers to a lack of growth or development.
* Decay: This implies a process of deterioration, the opposite of renewal.
* Extinction: This suggests a complete loss of something, the opposite of a revival.
If you're thinking of "Renaissance" as a specific event:
* Revolution: This is a significant change, but it may not necessarily be a revival or rebirth.
* Modernism: This is a distinct movement that came after the Renaissance, but it's not the opposite.
The best antonym will depend on your specific context.