supercritical fluid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A substance at a temperature above its critical point, having properties intermediate between those of a liquid and those of a gas.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics A substance at a temperature and pressure above its own thermodynamic critical point that can diffuse through solids like a gas and dissolve materials like a liquid.