Dictionary of the Irish language: based mainly on old and middle Irish materials. (1913-1976). Dublin: Royal Irish Academy. Online at: http://edil.qub.ac.uk/dictionary/search.php
Matasović, Ranko. Etymological Dictionary of Proto-Celtic. Indo-European Etymological Dictionaries Online. Edited by Alexander Lubotsky. Brill. Brill Online: http://iedo.brillonline.nl.ludwig.lub.lu.se/dictionaries/content/proto-celtic/index.html
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When the etymological tree is displayed in hierarchical style, the nodes can be repositioned manually only within their level.
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This map shows the etymological links in a geographic context.