Definition of exhaust:
to draw or let out wholly; to drain off completely; as, to exhaust the water of a well; the moisture of the earth is exhausted by evaporation; to empty by drawing or letting out the contents; as, to exhaust a well, or a treasury
"a decrepit, exhausted old man at fifty-five. --Motley."
system consisting of the parts of an engine through which burned gases or steam are discharged; the steam let out of a cylinder after it has done its work there