profundal
/prəˈfʌndl/Ecology
adjective
Designating or relating to regions of the water and bed of a lake where light penetration is insufficient to sustain photosynthesis.
noun
The profundal region of a lake.
Origin
Early 20th century; earliest use found in The Botanical Gazette. Apparently from classical Latin profundus profound + -al, probably after German Profundal, noun.