This is the 9501st most frequent Russian word.
усть
"Усть" translates to "mouth" or "estuary" (of a river) in English.
In this sentence, 'устье' refers to the mouth or opening of a river where it meets another body of water, used as a noun.
Устье реки покрыто льдом.
The river mouth is covered with ice.
Here, 'Усть' is part of a geographical name, indicating a location often situated at or near the mouth of a river.
Он вернулся из города Усть-Каменогорск.
He came back from the city of Ust-Kamenogorsk.
Again, 'устье' signifies the river's mouth, illustrating its specific use in describing natural features.