undefine-action removes the action specified by action-name from the action list specified by name-or-list. If the action specified by action-name does not exist, then this is handled according to the value of *handle-missing-action-in-action-list*.
name-or-list is evaluated to give either a list UID (to be looked up in the global registry of lists) or an action list object. action-name is a UID (general lisp object, to be compared by
equalp). It uniquely identifies this action within its list (as opposed to among all lists).
LispWorks User Guide and Reference Manual - 20 Sep 2017