windowbox

/W IH1 N D AW1 B AA1 K S/
noun
  1. 1

    A narrow box filled with earth, placed on a windowsill and used for growing plants.

  2. 2

    One of the hollows in the sides of a window frame for the weights which counterbalance a lifting sash.

Source: https://en.wiktionary.org/wiki/window%20box, https://en.wiktionary.org/wiki/windowbox