diff --git a/modules/tools/lookup/README.org b/modules/tools/lookup/README.org
index 05fdda993..b69d6b25e 100644
--- a/modules/tools/lookup/README.org
+++ b/modules/tools/lookup/README.org
@@ -10,6 +10,7 @@
 - [[#prerequisites][Prerequisites]]
   - [[#macos][MacOS]]
   - [[#arch-linux][Arch Linux]]
+  - [[#nixos][NixOS]]
 - [[#features][Features]]
   - [[#jump-to-definition][Jump to definition]]
   - [[#find-references][Find references]]
@@ -32,10 +33,11 @@ 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.
++ Support for online (and offline) dictionaries and thesauruses.
 
 ** Module Flags
 + ~+dictionary~ Enable word definition and thesaurus lookup functionality.
+  + ~+offline~ Install and prefer offline dictionary/thesaurus.
 + ~+docsets~ Enable integration with Dash.app docsets.
 
 ** Plugins
@@ -46,13 +48,13 @@ up definitions, references and documentation.
 * Prerequisites
 This module has several soft dependencies:
 
-+ ~ripgrep~ as a last-resort fallback for
-  jump-to-definition/find-references.
++ ~ripgrep~ as a last-resort fallback for jump-to-definition/find-references.
 + ~sqlite3~ for Dash docset support.
++ ~wordnet~ for offline dictionary and thesaurus support.
 
 ** MacOS
 #+BEGIN_SRC sh
-brew install ripgrep
+brew install ripgrep wordnet
 
 # An older version of sqlite is included in MacOS. If it causes you problems (and
 # folks have reported it will), install it through homebrew:
@@ -65,6 +67,16 @@ export PATH="/usr/local/opt/sqlite/bin:$PATH"
 ** Arch Linux
 #+BEGIN_SRC sh
 sudo pacman -S sqlite ripgrep
+sudo yay -S wordnet-cli
+#+END_SRC
+
+** NixOS
+#+BEGIN_SRC nix
+environment.systemPackages = with pkgs; [
+  ripgrep
+  sqlite
+  wordnet
+];
 #+END_SRC
 
 * Features
diff --git a/modules/tools/lookup/autoload/lookup.el b/modules/tools/lookup/autoload/lookup.el
index 3ee8f0cf4..352a1d4bc 100644
--- a/modules/tools/lookup/autoload/lookup.el
+++ b/modules/tools/lookup/autoload/lookup.el
@@ -321,12 +321,17 @@ Otherwise, falls back on `find-file-at-point'."
    (list (or (doom-thing-at-point-or-region 'word)
              (read-string "Look up in dictionary: "))
          current-prefix-arg))
+  (message "Looking up definition for %S" identifier)
   (cond ((and IS-MAC (require 'osx-dictionary nil t))
          (osx-dictionary--view-result identifier))
-        ((and +lookup-dictionary-enable-online (require 'define-word nil t))
-         (message "Looking up definition of %S" identifier)
+        ((and +lookup-dictionary-prefer-offline
+              (require 'wordnut nil t))
+         (unless (executable-find wordnut-cmd)
+           (user-error "Couldn't find %S installed on your system"
+                       wordnut-cmd))
+         (wordnut-search identifier))
+        ((require 'define-word nil t)
          (define-word identifier nil arg))
-        ;; TODO Implement offline dictionary backend
         ((user-error "No dictionary backend is available"))))
 
 ;;;###autoload
@@ -335,10 +340,13 @@ Otherwise, falls back on `find-file-at-point'."
   (interactive
    (list (doom-thing-at-point-or-region 'word) ; TODO actually use this
          current-prefix-arg))
-  (unless (require 'powerthesaurus nil t)
-    (user-error "No dictionary backend is available"))
-  (unless +lookup-dictionary-enable-online
-    ;; TODO Implement offline synonyms backend
-    (user-error "No offline dictionary implemented yet"))
   (message "Looking up synonyms for %S" identifier)
-  (powerthesaurus-lookup-word-dwim))
+  (cond ((and +lookup-dictionary-prefer-offline
+              (require 'synosaurus nil t))
+         (unless (executable-find synosaurus-wordnet--command)
+           (user-error "Couldn't find %S installed on your system"
+                       synosaurus-wordnet--command))
+         (synosaurus-choose-and-replace))
+        ((require 'powerthesaurus nil t)
+         (powerthesaurus-lookup-word-dwim))
+        ((user-error "No thesaurus backend is available"))))
diff --git a/modules/tools/lookup/config.el b/modules/tools/lookup/config.el
index 9116fb83e..59a5e93c4 100644
--- a/modules/tools/lookup/config.el
+++ b/modules/tools/lookup/config.el
@@ -85,15 +85,15 @@ 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
+(defvar +lookup-dictionary-prefer-offline (featurep! +offline)
   "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'.
+Used by `+lookup/dictionary-definition' and `+lookup/synonyms'.
 
-For `+lookup/word-definition', this is ignored on Mac, where Emacs users
+For `+lookup/dictionary-definition', this is ignored on Mac, where Emacs users
 Dictionary.app behind the scenes to get definitions.")
 
 
@@ -196,3 +196,7 @@ See https://github.com/magit/ghub/issues/81"
   (define-key! text-mode-map
     [remap +lookup/definition] #'+lookup/dictionary-definition
     [remap +lookup/references] #'+lookup/synonyms))
+
+
+;;;###package synosaurus
+(setq synosaurus-choose-method 'default) ; use ivy/helm instead of ido
diff --git a/modules/tools/lookup/packages.el b/modules/tools/lookup/packages.el
index 288d779c7..e80c98361 100644
--- a/modules/tools/lookup/packages.el
+++ b/modules/tools/lookup/packages.el
@@ -24,7 +24,9 @@
 (when (featurep! +dictionary)
   (if IS-MAC
       (package! osx-dictionary :pin "1b79ff64c7")
-    (package! define-word :pin "d8c76d503b"))
-  ;; Need for Google/DuckDuckGo auto-completion on `+lookup/online'
-  (package! powerthesaurus :pin "81a262ec0c")
-  (package! request :pin "4be823a89b"))
+    (package! define-word :pin "d8c76d503b")
+    (package! powerthesaurus :pin "81a262ec0c")
+    (package! request :pin "4be823a89b")
+    (when (featurep! +offline)
+      (package! wordnut :pin "feac531404")
+      (package! synosaurus :pin "14d34fc92a"))))