diff --git a/docs/index.org b/docs/index.org
index a623084de..eff52c0cd 100644
--- a/docs/index.org
+++ b/docs/index.org
@@ -237,7 +237,8 @@ Small modules that give Emacs access to external tools & services.
 + flycheck - Live error/warning highlights
 + flyspell - Spell checking
 + gist - TODO
-+ [[file:../modules/tools/lookup/README.org][lookup]] =+docsets= - Universal jump-to & documentation lookup backend
++ [[file:../modules/tools/lookup/README.org][lookup]] =+dictionary +docsets= - Universal jump-to & documentation lookup
+  backend
 + [[file:../modules/tools/lsp/README.org][lsp]] - TODO
 + macos - TODO
 + magit - TODO
diff --git a/modules/tools/lookup/README.org b/modules/tools/lookup/README.org
index 53d7feb4b..c541cba8b 100644
--- a/modules/tools/lookup/README.org
+++ b/modules/tools/lookup/README.org
@@ -32,8 +32,10 @@ up definitions, references and documentation.
 + Documentation lookup for a variety of online sources (like devdocs.io,
   stackoverflow or youtube).
 + Integration with Dash.app docsets.
++ Support for online dictionaries and thesauruses.
 
 ** Module Flags
++ ~+dictionary~ Enable word definition and thesaurus lookup functionality.
 + ~+docsets~ Enable integration with Dash.app docsets.
 
 ** Plugins
diff --git a/modules/tools/lookup/autoload/lookup.el b/modules/tools/lookup/autoload/lookup.el
index 46726eca0..a2ba7a534 100644
--- a/modules/tools/lookup/autoload/lookup.el
+++ b/modules/tools/lookup/autoload/lookup.el
@@ -320,3 +320,47 @@ Otherwise, falls back on `find-file-at-point'."
                               (run-hooks 'projectile-find-file-hook))))
                          (#'doom-project-browse))))
              (find-file-at-point path))))))
+
+
+;;
+;;; Dictionary
+
+;;;###autoload
+(defun +lookup/word-definition (identifier &optional arg)
+  "Look up the definition of the word at point (or selection)."
+  (interactive
+   (list (+lookup-symbol-or-region)
+         current-prefix-arg))
+  (unless (featurep! +dictionary)
+    (user-error "The +dictionary feature hasn't be enabled on :tools lookup module"))
+  (cond (IS-MAC
+         (osx-dictionary-search-input identifier))
+        (+lookup-dictionary-enable-online
+         (define-word identifier nil arg))
+        ;; TODO Implement offline dictionary backend
+        ((user-error "No offline dictionary defined yet"))))
+
+;;;###autoload
+(defun +lookup/word-synonyms (identifier &optional arg)
+  "Look up and insert a synonym for the word at point (or selection)."
+  (interactive
+   (list (+lookup-symbol-or-region)
+         current-prefix-arg))
+  (unless (featurep! +dictionary)
+    (user-error "The +dictionary feature hasn't be enabled on :tools lookup module"))
+  (if +lookup-dictionary-enable-online
+      (request
+        (powerthesaurus-compose-url identifier)
+        :parser (lambda () (libxml-parse-html-region (point) (point-max)))
+        :headers '(("User-Agent" . "Chrome/74.0.3729.169"))
+        :success (cl-function
+                  (lambda (&key data &allow-other-keys)
+                    ;; in order to allow users to quit powerthesaurus prompt
+                    ;; with C-g, we need to wrap callback with this
+                    (with-local-quit
+                      (funcall (powerthesaurus-choose-callback
+                                (region-beginning) (region-end))
+                               (powerthesaurus-pick-synonym data)
+                               identifier)))))
+    ;; TODO Implement offline synonyms backend
+    (user-error "No offline dictionary implemented yet")))
diff --git a/modules/tools/lookup/config.el b/modules/tools/lookup/config.el
index a34773187..c80e09c52 100644
--- a/modules/tools/lookup/config.el
+++ b/modules/tools/lookup/config.el
@@ -84,6 +84,17 @@ If the argument is interactive (satisfies `commandp'), it is called with
 argument: the identifier at point. See `set-lookup-handlers!' about adding to
 this list.")
 
+(defvar +lookup-dictionary-enable-online t
+  "If non-nil, look up dictionaries online.
+
+Setting this to nil will force it to use offline backends, which may be less
+than perfect, but available without an internet connection.
+
+Used by `+lookup/word-definition' and `+lookup/word-synonyms'.
+
+For `+lookup/word-definition', this is ignored on Mac, where Emacs users
+Dictionary.app behind the scenes to get definitions.")
+
 
 ;;
 ;;; dumb-jump
@@ -165,3 +176,22 @@ See https://github.com/magit/ghub/issues/81"
 
   (use-package! counsel-dash
     :when (featurep! :completion ivy)))
+
+
+;;
+;;; Dictionary integration
+
+(use-package! define-word
+  :when (featurep! +dictionary)
+  :unless IS-MAC
+  :defer t
+  :config
+  (setq define-word-displayfn-alist
+        (cl-loop for (service . _) in define-word-services
+                 collect (cons service #'+eval-display-results-in-popup))))
+
+
+(when (featurep! +dictionary)
+  (define-key! text-mode-map
+    [remap +lookup/definition] #'+lookup/word-definition
+    [remap +lookup/references] #'+lookup/word-synonyms))
diff --git a/modules/tools/lookup/packages.el b/modules/tools/lookup/packages.el
index 6c0b50565..92113d696 100644
--- a/modules/tools/lookup/packages.el
+++ b/modules/tools/lookup/packages.el
@@ -23,3 +23,9 @@
     (package! helm-dash))
   (when (featurep! :completion ivy)
     (package! counsel-dash)))
+
+(when (featurep! +dictionary)
+  (if IS-MAC
+      (package! osx-dictionary)
+    (package! define-word))
+  (package! powerthesaurus))