not easily perturbed or excited or upset; marked by extreme calm and composure; "hitherto imperturbable, he now showed signs of alarm"; "an imperturbable self-possession"; "unflappable in a crisis"
(cryogenics) the lowest temperature theoretically attainable (at which the kinetic energy of atoms and molecules is minimal); 0 Kelvin or -273.15 centigrade or -459.67 Fahrenheit
showing the way by conducting or leading; imposing direction on; "felt his mother's directing arm around him"; "the directional role of science on industrial progress"