Spelling fix.

lisp/calendar/appt.el

@@ -225,7 +225,7 @@ If this is non-nil, appointment checking is active.")
 The string STRING describes the appointment, due in integer MINS minutes.
 The format of the visible reminder is controlled by `appt-display-format'.
 The variable `appt-audible' controls the audible reminder."
-  ;; Let-binding for backwards compatability.  Remove when obsolete
+  ;; Let-binding for backwards compatibility.  Remove when obsolete
   ;; vars appt-msg-window and appt-visible are dropped.
   (let ((appt-display-format
          (if (eq appt-display-format 'ignore)

lisp/calendar/diary-lib.el

@@ -797,7 +797,7 @@ LIST-ONLY is non-nil, in which case it just returns the list."
             (unless list-only
               (if (and diary-display-function
                        (listp diary-display-function))
-                  ;; Backwards compatability.
+                  ;; Backwards compatibility.
                   (run-hooks 'diary-display-function)
                 (funcall (or diary-display-function
                              'diary-simple-display))))