In the Options dialog of Backword, copy some of the following links to the setting 'Search Web'.
Search engines shows an explanation of a word in:

• Seznam http://slovnik.seznam.cz/?lang=en_cz&q=
• Slovník online http://www.online-slovnik.cz/?translate-type=en-cz&match-type=start&ignore-diacritic=1&word=
• Sms.cz http://slovniky.sms.cz/index.php?P_id_kategorie=65456&P_soubor=%2Fslovniky%2Findex.php%3Fbjvolba%3Den_cz%26send_data%3D1%26word%3D

• Etymology: http://www.etymonline.com/index.php?search=
• Comprehensive http://www.answers.com/
• Slang http://www.urbandictionary.com/define.php?term=
• Thesaurus http://www.thefreedictionary.com/dict.asp?Word=
• Word Associations http://www.wordassociation.org/search/ (find out how English speakers associate the words they know)
• Greek/Latin Etymology: http://wordinfo.info/words/index.php?v=info&a=view_results&s=
• Dictionary.com: http://dictionary.reference.com/browse/
• Merriam-Webster: http://www.m-w.com/dictionary/
• English definitions: http://www.onelook.com/?ls=a&w=

• wordreference.com http://www.wordreference.com/enfr/

• http://dict.leo.org/ende?lp=ende〈=de&searchLoc=0&cmpType=relaxedªHdr=on&spellToler=on&relink=off&search=

• wordreference.com http://www.wordreference.com/enit/

• Shogakukan (livedoor) http://dic.livedoor.com/search?kind=1&type=0&key=
• Shogakukan (yahoo) http://dic.yahoo.co.jp/dsearch?dtype=2&p=
• Sanseido (goo) http://dictionary.goo.ne.jp/search.php?kind=ej&MT=
• Kenkyuusha (excite) http://www.excite.co.jp/dictionary/english_japanese/?match=beginswith&dic=enja&search=
• ALC http://www2.alc.co.jp/ejr/index.php?word_in2=%A4%AB%A4%AD%A4%AF%A4%B1%A4%B3&word_in3=PVawEWi72JXCKoa0Je&word_in=
• Babylon http://info.babylon.com/onlinebox.cgi?tl=JA&rt=ol&uil=EN&cid=&term=

• Naver Dictionary Search http://endic.naver.com/search.nhn?x=0&y=0&kind=keyword&query= (this will search the english-korean dictionary for the word following "query=")
  

• Stardict http://www.stardict.org/query.php?q=
• Babelon http://info.babylon.com/onlinebox.cgi?tl=FR&rt=ol&uil=EN&cid=&term=

1. "NL" > Dutch
2. "DE" > German
3. "PT" > Portuguese
4. "SR" > Serbian
5. "HR" > Croatian
6. "FR" > French
7. "HE" > Hebrew
8. "ES" > Spanish
9. "JA" > Japanese
10. "IT" > Italian
11. "ZHS" > Chinese (s)
12. "ZHT" > Chinese (t)
13. "KO" > Korean
14. "RU" > Russian
15. "SV" > Swedish
16. "TR" > Turkish
17. "OT" > Additional...

• dict.cn http://sh.dict.cn/search/?q=
• Kingsoft ciba http://www.iciba.com/search?s=

• Google http://translate.google.com/translate_t?langpair=en|es&hl=es&ie=UTF-8&prev=/language_tools&text=
• wordreference.com http://www.wordreference.com/es/translation.asp?tranword=

• Yahoo奇摩字典 http://tw.dictionary.yahoo.com/search?ei=UTF-8&p=
• hkYahoo字典 http://hk.dictionary.yahoo.com/search.html?s=

Other search engines

• Acronym Finder http://www.acronymfinder.com/af-query.asp?Acronym=
• OneLook http://www.onelook.com/?w=
• del.icio.us Search http://del.icio.us/search/?all=

• Google http://www.google.com/search?&q=
• Google Images http://images.google.com/images?q=