• (n.) An instrument for recording simultaneously the pressure and temperature of a gas; a combined thermograph and barograph.
Ther`mo·bar'o·graph noun (Physics) An instrument for recording simultaneously the pressure and temperature of a gas; a combined thermograph and barograph. 
thermobarograph 1. In physics, an instrument for recording simultaneously the pressure and temperature of a gas; a combination of a thermograph and a barograph. 2. An instrument that simultaneously records temperature as well as atmospheric pressure.