कड़ा बनाना
A starch to stiffen fabrics

मजबूत होना  =  occur
His resolution stiffened in response to her opposition.

मजबूत करना
The threat of punishment has only stiffened their resolve (= made them even more determined to do sth).

कड़ा कर लेना
She stiffened her body in anticipation.

कड़ा पड़ जाना
My muscles had stiffened up after the climb.

तान लेना
I stiffened my back and faced him.

अकड़ जाना
She stiffened with fear.