incoercible

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Difficult or impossible to coerce or control forcibly: incoercible rebel leaders.

Century Dictionary and Cyclopedia

1. Not to be coerced or compelled; incapable of being constrained or forced.
2. In physics, incapable of being reduced to a liquid form by any amount of pressure. Certain gases were formerly supposed to have this property. See gas.
3. In physical:
4. Incapable of reduction to tangible condition by pressure: applied to forms of energy, such as heat and electricity, when they were thought of as extremely subtile fluids.

Wiktionary

1. adj. Not to be coerced; incapable of being compelled or forced.
2. adj. physics, of a gas Not capable of being reduced to liquid form by pressure.
3. adj. physics, archaic That cannot be confined in, or excluded from, vessels, like ordinary fluids, gases, etc.; said of heat, light, electricity, etc.

GNU Webster's 1913

1. adj. Not to be coerced; incapable of being compelled or forced.
2. adj. (Physics) Not capable of being reduced to the form of liquid by pressure; -- said of any gas above its critical temperature.
3. adj. (Physics) That can note be confined in, or excluded from, vessels, like ordinary fluids, gases, etc.; -- said of the imponderable fluids, heat, light, electricity, etc.