Question

Nathan laughs when his grandfather describes him as a "cool cat." "that's how we used to describe someone who is neat, pleasing, good," his grandfather says. "not anymore," nathan replies. this exchange reminds us that language is __________

Answer 1

I believe the answer is: Arbitary

Arbitary in this context refers to a fact that a word in a certain language could be perceived differently by one person to another.
Factors that could influence this different perception could include things such as age, culture, experience, etc.