a layer of water between the warmer, surface zone and the colder, deep-water zone in a thermally stratified body of water, in which the temperature decreases rapidly with depth
Origin:
thermo- + -cline, as in anticline
See thermocline in American Heritage Dictionary 4
noun
A layer in a large body of water, such as a lake, that sharply separates regions differing in temperature, so that the temperature gradient across the layer is abrupt.