In math, when you care about the details of how small one thing is compared to some other thing, you probably use little-o notation. It's the same thing you're probably familiar with from computer science.

So if y is small compared to x, you might say y = o(x), or if it's really small compared to x, you might say y = o(x²), or if it's really really really small, o(x⁶)... whatever you need for your proof.

(o(x²) is more impressively small than o(x) because x < 1)