A dictionary tool which can switch Mac dictionary, sdic and commandline-dictionary-app.

init.el

;; http://www.namazu.org/~tsuchiya/sdic/index.html
(require 'sdic)

;; hg clone http://hg.pqrs.org/commandline-dictionary-app
(defvar dict-bin "/Users/masutaka/repository/commandline-dictionary-app/src/dict"
  "a path of commandline-dictionary-app")

(defun dictionary-app (word)
  "Display the meaning of word using Dictionary.app."
  (interactive (list (sdic-read-from-minibuffer)))
  (set-buffer (get-buffer-create sdic-buffer-name))
  (or (string= mode-name sdic-mode-name) (sdic-mode))
  (setq buffer-read-only nil)
  (erase-buffer)
  (insert (format "============================================================\n%s\n" word))
  (call-process dict-bin
                nil sdic-buffer-name t word
                "Japanese-English" "Japanese" "Japanese Synonyms")
  (setq buffer-read-only t)
  (set-buffer-modified-p nil)
  (sdic-display-buffer 0))

(defun dictionary-search (word)
  (browse-url
   (concat "dict:///" (url-hexify-string word))))

(defun my-dictionary (arg)
  (interactive "P")
  (cond
   ((equal arg '(16))
    (dictionary-app (sdic-read-from-minibuffer)))
   ((equal arg '(4))
    (sdic-describe-word (sdic-read-from-minibuffer)))
   (t
    (dictionary-search (sdic-read-from-minibuffer)))))

The detail is the following.
http://masutaka.net/chalow/2012-09-17-1.html