Not sure if absolute economy size is really relevant. You could have 20 billion really poor people. You could have 19.9999 really poor people and one really rich one. I would consider both of those poor.
On the same note, the gini index is a kind of inequality measure. If your definition for "poor country" is one with uneven income distribution then the US is one of the poorest countries in the world. Like I don't know, I just don't feel like this definition of "poor" works.