The word is a modern scientific coinage, a portmanteau created in the mid-20th century. It fuses the Greek root therm- (heat) with a modified form of the word "resistor". The suffix -istor was chosen to echo the ending of "resistor" and "transistor", establishing it within the lexicon of electronic components. Thus, the term's literal construction as a "heat resistor" directly and logically describes its function as a device whose electrical resistance is thermally sensitive.

Structure: therm (heat) + istor (device/agent) - therm: From Greek thermē, meaning "heat". Functions as the core semantic root. - istor: A variant of the suffix -istor, derived from the agent noun suffix -ist and the instrumental suffix -or. It denotes a device or agent that performs a specific function.