One popular book on English mythology was published in 1957 by Brian Branston: The Lost Gods of England. This is an easy to read work and is full of useful and interesting information but it is not without fault. Whilst discussing Thunor Branston makes this partly erroneous observation:
"Thunor means `thunder`. The god was christened[if the verb is permissable] in the lower Rhineland although one could not say that he was born there. It was at a time when Saxons and Celts were rubbing shoulders: they traded goods, they traded ideas and they traded gods. The name Thunor I take to come from the second element of Celtic Jupiter Tanarus, the `Thundering Jupiter` and it must have been adopted into a Saxon dialect during the period before the North West European Sound Shift, that is, before A.D. 1."
There is no evidence whatsoever to deduce that the Germanic Thunor`s name has its origins in the Celtic Tanarus. That is simply bad scholarship. He presumes a great deal and expects us take his presumptions as scholarly fact!
"Taranis is cognate with the u-stem *taranu- seen in Old Irish torann, Welsh taran `thunder`. The Celtic taran- is metathetic for tanar-(= Germanic *thunar- `thunder`)" [Comparative Mythology, Jaan Puhvel, 1987]
Simply put, both the Celts and the Teutons named their Thunder God after their respective terms for `thunder`. It does not in way imply a borrowing one from the other. There could be grounds of course to assume that both Taranis and Thunor descended from a common Celto-Germanic form. In fact this to a certain extent makes some sense as both the Slavs and the Balts named their Thunder deity after Perkunas[and its many variants] which has its origins in the Proto-Indo-European *Perkunos, loosely named after the concept of the oak tree rather than thunder. So in this sense the Celts and the Teutons have a closer affinity.
Branston also appears to be rather reluctant to use the term `Germanic` or `Teutonic`, preferring instead to use the ridiculous and cumberson `North West European`!
"It is important, if we are to understand our own mythology, to explore the relationship existing between the northern peoples, that branch of the Indo-European speakers who were the ancestors of the present day Germans, Frisians, Dutch, Danes, Swedes, Norwegians, Icelanders and English. This group has been called in the past the Germanic or Teutonic nations: both names are ambiguous, for a part has come to be used for the whole, while both terms have an undesireable emotional colouring. I therefore propose to use a phrase formed in the same way as `Indo-European` and to call the ancestors of the Germans, Frisians, Dutch, Danes, Swedes, Norwegians, Icelanders and English after the part of the continent we first find them inhabiting in historical times the `North West Europeans`".The emphasis is mine. Thank the Gods that his ridiculous notion did not catch on even in the politically correct and stifling halls of acadaemia!