Removing \M-t keybinding

When I compose mail, I sometimes press \M-t to transpose words.  (The standard
keybinding for transpose-words in Emacs.)  But in WL, it runs wl-toggle-plugged,
so I accidentally go to offline mode.  I want to remove the \M-t binding.  I
tried

(add-hook 'wl-folder-mode-hook
			 '(lambda ()
				 (...)
             (define-key wl-folder-mode-map (kbd "\M-t") 'transpose-words)))

and

(add-hook 'wl-summary-mode-hook
			 '(lambda ()
				 (...)
             (define-key wl-summary-mode-map (kbd "\M-t") 'transpose-words)))

but neither works.  I also tried the same with mime-edit-mode-map, with no
success.

Any suggestions?