The American Heritage Dictionary of Indo-European Roots by Calvert Watkins 2001 (online version, Google Books)
The Oxford Dictionary of English Etymology 1991
Oxford English Dictionary
Indo-European Language and Culture: An Introduction by Benjamin Fortson
Indogermanisches etymologisches Wörterbuch by Julius Pokorny
Indo-European etymological dictionaries
Das Deutsche Wörterbuch von Jacob und Wilhelm Grimm
Sanskrit, Tamil and Pahlavi Dictionaries
digital dictionaries of south asia
Perseus Digital Library
Walde's Lateinisches etymologisches Wörterbuch
Bosworth and Toller Anglo-Saxon Dictionary
Anglo-Norman Dictionary
French dictionaries
Gaelic Dictionaries Online
Dwelly's Illustrated Gaelic-English Dictionary
zmjezhd's dictionary links
Linguistics Research Center
Wordorigins
Indic Scripts Index for Herbs and Spices
UCLA phonetics lab data
Dictionary of the Scots Language
Romani lexicon
Where can I look it up?
The Oxford Dictionary of English Etymology 1991
Oxford English Dictionary
Indo-European Language and Culture: An Introduction by Benjamin Fortson
Indogermanisches etymologisches Wörterbuch by Julius Pokorny
Indo-European etymological dictionaries
Das Deutsche Wörterbuch von Jacob und Wilhelm Grimm
Sanskrit, Tamil and Pahlavi Dictionaries
digital dictionaries of south asia
Perseus Digital Library
Walde's Lateinisches etymologisches Wörterbuch
Bosworth and Toller Anglo-Saxon Dictionary
Anglo-Norman Dictionary
French dictionaries
Gaelic Dictionaries Online
Dwelly's Illustrated Gaelic-English Dictionary
zmjezhd's dictionary links
Linguistics Research Center
Wordorigins
Indic Scripts Index for Herbs and Spices
UCLA phonetics lab data
Dictionary of the Scots Language
Romani lexicon
Where can I look it up?