diff --git a/src/AppleSpellChecker.h b/src/AppleSpellChecker.h
index e41ff3729d..64e5f2b26b 100644
--- a/src/AppleSpellChecker.h
+++ b/src/AppleSpellChecker.h
@@ -26,6 +26,7 @@ public:
 	//@{
 	enum Result check(WordLangTuple const &);
 	void suggest(WordLangTuple const &, docstring_list &);
+	void stem(WordLangTuple const &, docstring_list &) {};
 	void insert(WordLangTuple const &);
 	void remove(WordLangTuple const &);
 	void accept(WordLangTuple const &);
diff --git a/src/AspellChecker.h b/src/AspellChecker.h
index c2208498ec..bce5402b12 100644
--- a/src/AspellChecker.h
+++ b/src/AspellChecker.h
@@ -27,6 +27,7 @@ public:
 	//@{
 	enum Result check(WordLangTuple const &);
 	void suggest(WordLangTuple const &, docstring_list &);
+	void stem(WordLangTuple const &, docstring_list &) {};
 	void insert(WordLangTuple const &);
 	void remove(WordLangTuple const &);
 	void accept(WordLangTuple const &);
diff --git a/src/EnchantChecker.h b/src/EnchantChecker.h
index fc1b70b13a..d92774972d 100644
--- a/src/EnchantChecker.h
+++ b/src/EnchantChecker.h
@@ -33,6 +33,7 @@ public:
 	///@{
 	enum Result check(WordLangTuple const &);
 	void suggest(WordLangTuple const &, docstring_list &);
+	void stem(WordLangTuple const &, docstring_list &) {};
 	void insert(WordLangTuple const &);
 	void remove(WordLangTuple const &);
 	void accept(WordLangTuple const &);
diff --git a/src/HunspellChecker.cpp b/src/HunspellChecker.cpp
index d044889107..a2d2c95e05 100644
--- a/src/HunspellChecker.cpp
+++ b/src/HunspellChecker.cpp
@@ -413,6 +413,25 @@ void HunspellChecker::suggest(WordLangTuple const & wl,
 }
 
 
+void HunspellChecker::stem(WordLangTuple const & wl,
+	docstring_list & suggestions)
+{
+	suggestions.clear();
+	Hunspell * h = d->speller(wl.lang());
+	if (!h)
+		return;
+	string const encoding = h->get_dic_encoding();
+	string const word_to_check = to_iconv_encoding(wl.word(), encoding);
+	char ** suggestion_list;
+	int const suggestion_number = h->stem(&suggestion_list, word_to_check.c_str());
+	if (suggestion_number <= 0)
+		return;
+	for (int i = 0; i != suggestion_number; ++i)
+		suggestions.push_back(from_iconv_encoding(suggestion_list[i], encoding));
+	h->free_list(&suggestion_list, suggestion_number);
+}
+
+
 bool HunspellChecker::hasDictionary(Language const * lang) const
 {
 	if (!lang)
diff --git a/src/HunspellChecker.h b/src/HunspellChecker.h
index ca28d01d64..686f014384 100644
--- a/src/HunspellChecker.h
+++ b/src/HunspellChecker.h
@@ -27,6 +27,7 @@ public:
 	///@{
 	enum Result check(WordLangTuple const &);
 	void suggest(WordLangTuple const &, docstring_list &);
+	void stem(WordLangTuple const &, docstring_list &);
 	void insert(WordLangTuple const &);
 	void remove(WordLangTuple const &);
 	void accept(WordLangTuple const &);
diff --git a/src/SpellChecker.h b/src/SpellChecker.h
index f87ef122b9..425925ce37 100644
--- a/src/SpellChecker.h
+++ b/src/SpellChecker.h
@@ -62,6 +62,9 @@ public:
 	/// Gives suggestions.
 	virtual void suggest(WordLangTuple const &, docstring_list & suggestions) = 0;
 
+	/// Lemmatizing: return stem of word (used by Thesaurus).
+	virtual void stem(WordLangTuple const &, docstring_list & suggestions) = 0;
+
 	/// insert the given word into the personal dictionary
 	virtual void insert(WordLangTuple const &) = 0;
 
diff --git a/src/Thesaurus.cpp b/src/Thesaurus.cpp
index fcec80bef5..f8e8448979 100644
--- a/src/Thesaurus.cpp
+++ b/src/Thesaurus.cpp
@@ -15,9 +15,13 @@
 
 #include "LyXRC.h"
 
+#include "SpellChecker.h"
+#include "WordLangTuple.h"
+
 #include "support/FileNameList.h"
 #include "support/Package.h"
 #include "support/debug.h"
+#include "support/docstring_list.h"
 #include "support/filetools.h"
 #include "support/gettext.h"
 #include "support/lstrings.h"
@@ -195,17 +199,20 @@ bool Thesaurus::thesaurusInstalled(docstring const & lang) const
 }
 
 
-Thesaurus::Meanings Thesaurus::lookup(docstring const & t, docstring const & lang)
+Thesaurus::Meanings Thesaurus::lookup(WordLangTuple const & wl)
 {
 	Meanings meanings;
 	MyThes * mythes = 0;
 
-	if (!d->addThesaurus(lang))
+	docstring const lang_code = from_ascii(wl.lang()->code());
+	docstring const t = wl.word();
+
+	if (!d->addThesaurus(lang_code))
 		return meanings;
 
 	for (Thesauri::const_iterator it = d->thes_.begin();
 	     it != d->thes_.end(); ++it) {
-		if (it->first == lang) {
+		if (it->first == lang_code) {
 			mythes = it->second;
 			break;
 		}
@@ -220,8 +227,22 @@ Thesaurus::Meanings Thesaurus::lookup(docstring const & t, docstring const & lan
 	string const text = to_iconv_encoding(support::lowercase(t), encoding);
 	int len = strlen(text.c_str());
 	int count = mythes->Lookup(text.c_str(), len, &pmean);
-	if (!count)
-		return meanings;
+	if (!count) {
+		SpellChecker * speller = theSpellChecker();
+		if (!speller)
+			return meanings;
+		docstring_list suggestions;
+		speller->stem(wl, suggestions);
+		for (size_t i = 0; i != suggestions.size(); ++i) {
+			string const wordform = to_iconv_encoding(support::lowercase(suggestions[i]), encoding);
+			len = strlen(wordform.c_str());
+			count = mythes->Lookup(wordform.c_str(), len, &pmean);
+			if (count)
+				break;
+		}
+		if (!count)
+			return meanings;
+	}
 
 	// don't change value of pmean or count
 	// they are needed for the CleanUpAfterLookup routine
diff --git a/src/Thesaurus.h b/src/Thesaurus.h
index 9c0bdc61de..a479fda962 100644
--- a/src/Thesaurus.h
+++ b/src/Thesaurus.h
@@ -14,6 +14,7 @@
 #define THESAURUS_H
 
 #include "support/docstring.h"
+#include "WordLangTuple.h"
 
 #include <map>
 #include <string>
@@ -38,7 +39,7 @@ public:
 	/**
 	 * look up some text in the thesaurus
 	 */
-	Meanings lookup(docstring const & text, docstring const & lang);
+	Meanings lookup(WordLangTuple const & wl);
 	/** check if a thesaurus for a given language \p lang is available
 	 *  (installed and loaded)
 	 */
diff --git a/src/frontends/qt4/GuiThesaurus.cpp b/src/frontends/qt4/GuiThesaurus.cpp
index 86ed9598ab..cf6f3821cf 100644
--- a/src/frontends/qt4/GuiThesaurus.cpp
+++ b/src/frontends/qt4/GuiThesaurus.cpp
@@ -22,6 +22,7 @@
 #include "FuncRequest.h"
 #include "Language.h"
 #include "lyxfind.h"
+#include "WordLangTuple.h"
 
 #include "support/debug.h"
 #include "support/gettext.h"
@@ -173,11 +174,11 @@ void GuiThesaurus::updateLists()
 
 	QString const lang = languageCO->itemData(
 		languageCO->currentIndex()).toString();
-	docstring const lang_code =
-		from_ascii(lyx::languages.getLanguage(fromqstr(lang))->code());
+	Language * language = const_cast<Language*>(lyx::languages.getLanguage(fromqstr(lang)));
+	docstring const lang_code = from_ascii(language->code());
 
 	Thesaurus::Meanings meanings =
-		getMeanings(qstring_to_ucs4(entryCO->currentText()), lang_code);
+		getMeanings(WordLangTuple(qstring_to_ucs4(entryCO->currentText()), language));
 
 	for (Thesaurus::Meanings::const_iterator cit = meanings.begin();
 		cit != meanings.end(); ++cit) {
@@ -271,11 +272,10 @@ void GuiThesaurus::replace(docstring const & newstr)
 }
 
 
-Thesaurus::Meanings const & GuiThesaurus::getMeanings(docstring const & str,
-	docstring const & lang)
+Thesaurus::Meanings const & GuiThesaurus::getMeanings(WordLangTuple const & wl)
 {
-	if (str != laststr_)
-		meanings_ = thesaurus.lookup(str, lang);
+	if (wl.word() != laststr_)
+		meanings_ = thesaurus.lookup(wl);
 	return meanings_;
 }
 
diff --git a/src/frontends/qt4/GuiThesaurus.h b/src/frontends/qt4/GuiThesaurus.h
index 17f9ebf179..3cc45f0993 100644
--- a/src/frontends/qt4/GuiThesaurus.h
+++ b/src/frontends/qt4/GuiThesaurus.h
@@ -16,6 +16,8 @@
 #include "Thesaurus.h"
 #include "ui_ThesaurusUi.h"
 
+#include "WordLangTuple.h"
+
 class QTreeWidgetItem;
 
 namespace lyx {
@@ -56,8 +58,7 @@ private:
 	void replace(docstring const & newstr);
 
 	/// get meanings
-	Thesaurus::Meanings const & getMeanings(docstring const & str,
-		docstring const & lang);
+	Thesaurus::Meanings const & getMeanings(WordLangTuple const & wl);
 
 private:
 	/// last string looked up