refractory
Pronunciation: /rɪˈfrakt(ə)ri/
adjective
formal- 2resistant to a process or stimulus: some granules are refractory to secretory stimuli it will treat ores considered refractory to normal flotation methods
- Medicine (of a person, illness, or diseased tissue) not yielding to treatment: healing of previously refractory ulcers
- Medicine, rare (of a person or animal) resistant to infection: turkeys can be infected when young but are refractory as adults
- technical (of a substance) resistant to heat; hard to melt or fuse: refractory materials found in lunar samples

Origin:
early 17th century: alteration of obsolete refractary, from Latin refractarius 'stubborn' (see also refract)