the /ALL qualifier. Do not specify a window definition name with /ALL.

11.2  –  Qualifiers

11.2.1    /ALL

    Cancels all predefined and user-defined window definitions.

11.3  –  Description

    When a window definition is canceled, you can no longer use its
    name in a DISPLAY command. The CANCEL WINDOW command does not
    affect any displays.

    Related commands:

       (SHOW,CANCEL) DISPLAY
       (SET,SHOW) WATCH

11.4  –  Example

  DBG> CANCEL WINDOW MIDDLE

      This command permanently deletes the screen window definition
      MIDDLE.