efaq: Deleting menus and menu options
5.43 How do I delete menus and menu options?
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The simplest way to remove a menu is to set its keymap to ‘nil’. For
example, to delete the ‘Words’ menu (Modifying pull-down menus),
use:
(define-key global-map [menu-bar words] nil)
Similarly, removing a menu option requires redefining a keymap entry
to ‘nil’. For example, to delete the ‘Forward word’ menu option from
the ‘Edit’ menu (we added it in Modifying pull-down menus), use:
(define-key global-map [menu-bar edit forward] nil)