In my opinion, the theory suffers from a woeful dearth of evidence. There simply isn't enough material to evince us that mystery loanwords and ancient toponyms are Vasconic. But there is one example that makes me raise my eyebrows...
In 1905, a linguist by the name of Resurrección Azkue first noticed that many Basque words seemed to be comprised of the sound iz and other words. Azkue argued that *iz (the asterisk indicates that the word is a hypothetical, and not proven) meant water. It would make sense, right? Take a look at three of Azkue's reasons:
izerdi "sweat" = iz + erdi "half" (half-water)
Izpazter an oceanside territory and town (modern Ispaster) = iz + bazter "edge" (water-edge)
izurde "dolphin" = iz + urde "pig" (water-pig)
Sadly, the theory did not survive long. As R. L. Trask writes,
"But this putative stem was demolished by Michelena... who showed that most of these items had other and better etymologies. For example, izurde ‘dolphin’... stands alongside [the Lapurdian dialect of Basque] gizaurde, which is transparently a compound of gizon ‘man’ (regular combining form giza-) and urde. The unusual loss of initial /g/ is paralleled by the toponym recorded early as Giçairudiaga but modern Izurdiaga. Accordingly, there is no case for the reality of the putative *iz."So Michelena settled it. The reflex of izurde was *gizurde "man-pig." We can move on, right?
Enter Vennemann, who has made several interesting observations. First, the Basque love to make metaphorical designations of less important animals out of already existing words. Consider ur "water," which is used to make the words for seal (urxahal 'water-calf'); pike (uharts 'water-bear'); and otter (urtxakur 'water-dog') among many others.
Second, and more interestingly, Middle High Germanic had a very peculiar word for dolphin: merswin 'sea-swine.' What we have, then, is an old European parallel. Might this metaphor been a common one in ancient times? Did *iz- exist? If so, then what does Vennemann make of the Lapurdian spelling gizaurde which gives us a /g/?
So many questions and no answers!
- Vennemann, Theo. ""A Satisfactory Etymology has Long Been Available:" Notes on Vasconic Names Outside the Basque Country with Particular Reference to Some British Arn and Earn- Names and to German Arnoldsweiler." Anuario del seminario del filologia vasca "Julio de Urquijo". XL: 1-2. 2006.
- Trask, R. L. *iz in Etymological Dictionary of Basque. Ed. by Max Wheeler. University of Sussex. 2008.
- Azkue, Resurreccion Maria de. Diccionario vasco-espanol-francés/Dictionnaire basque-espagnol-français. Geuthner. 1905.