line connecting points of equal temperature at a given ocean depth
• (n.) A line drawn through points of equal temperature in a vertical section of the ocean.
I`so·ther'mo·bath noun [ Iso- + Greek ... hot + ... depth.] (Physics Geog) A line drawn through points of equal temperature in a vertical section of the ocean. 
isothermobath A line connecting points having the same temperature in a diagram of a vertical section of the ocean.
a line drawn on a diagram of a vertical section of the ocean connecting all points having equal temperature.