Definitions

1. verb

to sink or settle down into something, especially a hole or depression, in a way that makes it harder to get out, or to become submerged in something

“The ship countersank into the mud, making it impossible to free it.”

2. noun

the act of sinking or settling down into something, especially a hole or depression, in a way that makes it harder to get out

“The countersank of the ship was too deep for the rescue team to reach.”