epilimnion

noun

epi·​lim·​ni·​on ˌe-pə-ˈlim-nē-ˌän 

-nē-ən

: the water layer overlying the thermocline of a lake

Word History

Etymology

epi- + Greek límnē "standing water, pool, marshy lake" + -ion, noun suffix — more at limnetic

Note: See note at hypolimnion.

First Known Use

circa 1910, in the meaning defined above