Curse of the Sphinx (Patreon)

Looks like demigod Nico in a pickle when the local museum acquires a new exhibit that takes over the city. If he can't solve the riddle then he's gonna join the others as permanent additions to the sphinx's servants.

The riddle goes-

Four letters stand to make my name,

Should two be taken four remains,

And if they should take away one more,

My meaning will be as before.

what am I?