Isobar

Part of speech: noun (n.)

A line connecting or marking places upon the surface of the earth where height of the barometer reduced to sea level is the same either at a given time, or for a certain period (mean height), as for a year; an isopiestic line. [Written also isobare.]

Part of speech: noun (n.)

The quality or state of being equal in weight, especially in atmospheric pressure. Also, the theory, method, or application of isobaric science.