Strong/Powerful:
* बलवान (balwaan) - This is a general term for strong.
* शक्तिशाली (shaktishali) - This implies powerful and capable.
* सशक्त (sashakt) - This suggests a powerful presence or influence.
Healthy/Robust:
* स्वस्थ (svasth) - This refers to good health.
* तंदुरुस्त (tandurust) - This signifies robust health.
* हृष्ट-पुष्ट (hrishta-pusht) - This means healthy and strong.
Brave/Courageous:
* बहादुर (bahaadur) - This implies bravery.
* निडर (nider) - This refers to fearlessness.
* साहसी (sahaasi) - This means courageous.
The best opposite word for "दुर्बल" would depend on the specific meaning you are trying to convey.