the coldest period in the winter / a winter that's colder than that in a normal year

protection against the cold

To perform; to do; to conduct oneself; to carry out.

plan, measure, step, countermeasure

tight / reliable

stable, fulfilled

be fast, securely in place / be reliable, level-headed / keep going, keep trying

duration, period

fast (in a firm or secure manner), tightly / surely, unwaveringly, steadily, reliably

needed, necessary