What is always in front of you, but can never be seen?

Shapeless I stand, yet I bar the way, I exist in the mind, but not in the day. I hold without hands, I bind without thread, And once I am known, my power has fled

I turn every leap into a curve, yet never take a step. I hold the oceans without a cup and pin the mountains to their beds. I hold the moon without hands And make your body speak in numbers.

The first two letters signify a male, the first three letters signify a female, the first four letters signify a great, while the entire word signifies a great woman. What is the word?

A rich man needs it, a poor man has it, if we eat it, we die, and when we die, we bring it with us.