Question

why cannot we define cold​

Answer 1

Explanation:

We cannot define cold because that is a feeling of touch or sensation experienced by the skin and nervous system of a human body.  

At a particular temperature, one person might feel cold with the surrounding temperature getting cool and at the same time, another person might find the temperature pleasant or still hot.  

So it is not a measure but a feeling deferentially defined from one person to another at a particular temperature.