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海底， かいてい， うなぞこ
1. bottom of the ocean, seafloor, seabed
2. undersea, submarine
tbd
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沈む， しずむ
1. to sink, to go under, to submerge
2. to go down (e.g. sun), to set, to descend
3. to feel depressed, to become subdued, to become somber
下沉，沉没，淹没；感到沮丧，变得低落，变得阴郁
に
1. at (place, time), in, on, during
2. to (direction, state), toward, into
3. for (purpose)
4. because of (reason), for, with
5. by, from
6. as (i.e. in the role of)
7. per, in, for, a (e.g. "once a month")
8. and, in addition to
9. if, although
tbd