What is "to cave in"

Cave \Cave\, v. i.

1. To dwell in a cave. [Obs.]
   --Shak.

2. [See To cave in, below.] To fall in or down; as, the sand bank caved. Hence (Slang), to retreat from a position; to give way; to yield in a disputed matter. To cave in. [Flem. inkalven.]

   1. To fall in and leave a hollow, as earth on the side of a well or pit.

   2. To submit; to yield. [Slang]
      --H. Kingsley. [1913 Webster] ||