Not able to be changed or adapted to circumstances.
Not willing to change, e.g. one's opinion or habits.
Not flexible; not capable of bending or being bent.
Incapable of registering a reaction or stimulus.
Obstinate and unruly; strongly opposed to something.
Not affected by great heat.
Difficult to treat.
A material or piece of material, such as a brick, that has a very high melting point.