subatmospheric

[ suhb-at-muh s-fer-ik, -feer- ]
/ ˌsʌb æt məsˈfɛr ɪk, -ˈfɪər- /

adjective

(of a quantity) having a value lower than that of the atmosphere: subatmospheric temperatures.

Origin of subatmospheric

First recorded in 1940–45; sub- + atmospheric