Solids

From Memory Alpha, the free Star Trek reference.

"Solid" is the Changeling term for monoform humanoids who are not capable of changing their form at will. The Founders, after constant persecution at the hands of Solids, actively sought to bring "order" to the galaxy by controlling all Solids through the Jem'Hadar and Vorta. (DS9: "The Search, Part II")

The Changelings have the power to turn one of their own into a solid, which is used as a punishment for a severe crime. (DS9: "Broken Link")