the mixture of gases that surrounds the earth

वायु

English Usage: She took a deep breath of fresh air.

Hindi Usage: उसने ताजगी भरी वायु की गहरी साँस ली।

the process of becoming hard or solid

कठोरता

English Usage: The hardening of the material takes place at high temperatures.

Hindi Usage: सामग्री की कठोरता उच्च तापमान पर होती है।

to make or become hard

कठोर बनाना

English Usage: He is hardening the clay for the sculpture.

Hindi Usage: वह मूर्ति के लिए मिट्टी को कठोर बना रहा है।