The Collaborative International Dictionary
Thermostable
Thermostable \Ther`mo*sta"ble\, a. [Thermo- + stable fixed.] (Physiol. Chem.) Capable of being heated to or somewhat above 55[deg] C. without loss of special properties; -- said of proteins, immune substances, etc.
Wiktionary
thermostable
a. Physically or chemically unaffected by high temperatures