Wiktionary
n. (context geology English) A hemispheric-scale long but narrow topographic depression of the seabed.
Wikipedia
The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor. Oceanic trenches are a distinctive morphological feature of convergent plate boundaries, along which lithospheric plates move towards each other at rates that vary from a few mm to over ten cm per year. A trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab. Trenches are generally parallel to a volcanic island arc, and about from a volcanic arc. Oceanic trenches typically extend below the level of the surrounding oceanic floor. The greatest ocean depth to be sounded is in the Challenger Deep of the Mariana Trench, at a depth of below sea level. Oceanic lithosphere moves into trenches at a global rate of about 3 km/yr.
Usage examples of "oceanic trench".
Two of its massive fuel bladders are punctured as the weight of its hull drags the shattered ship into the third deepest oceanic trench in the world.
It wasn't cold, but cooler water flowing from the depths of the oceanic trench obviously found its way up here.
The silence felt deep, too, as though the guardian were calling from the bottom of an oceanic trench.
You're worried that this white dwarf is just like the oceanic trench on Jijo .
The study had the deep-fathom ambience of an oceanic trench forever beyond the reach of the sun but dimly revealed by radiant anemones and luminous jellyfish.
Pressure built during the descent, as though Micky were aboard a bathysphere, dropping into an oceanic trench.