firyoudaoicibaDictYouDict[fir 词源字典]
fir: [14] As with many Indo-European tree-names, fir is a widespread term, but it does not mean the same thing wherever it occurs. Its prehistoric Indo-European ancestor was *perkos, which in Latin became quercus, the name for the ‘oak’. Nor was the application confined to southern Europe, for Swiss German has a related ferch ‘oak wood’. But by and large, the Germanic languages took the term over and applied it to the ‘pine’: German föhre, Swedish fura, and Danish fyr all mean ‘pine’.

So also did Old English furh (known only in the compound furhwudu ‘pinewood’), but this appears to have died out. It was replaced semantically by pine, but formally by Middle English firre, a borrowing from the Old Norse form fyri- (also known only in compounds). This was used as a name not for the ‘pine’, but for the ‘fir’ (which in Old English times had been called sæppe or gyr).
[fir etymology, fir origin, 英语词源]
fir (n.)youdaoicibaDictYouDict
late 14c., from Old Norse fyri- "fir" or Old Danish fyr, both from Proto-Germanic *furkhon (cognates: Old High German foraha, German Föhre "fir"), from PIE root *perkwu-, originally meaning "oak," also "oak forest," but never "wood" (cognates: Sanskrit paraktah "the holy fig tree," Hindi pargai "the evergreen oak," Latin quercus "oak," Lombardic fereha "a kind of oak"). Old English had a cognate form in furhwudu "pine wood" (only in glosses, for Latin pinus), but the modern English word is more likely from Scandinavian and in Middle English fyrre glosses Latin abies "fir," which is of obscure origin.

According to Indo-Europeanists Gamkrelidze and Ivanov, "The semantics of the term clearly points to a connection between 'oak' and mountainous regions, which is the basis for the ancient European term applied to forested mountains" (such as Gothic fairgunni "mountainous region," Old English firgen "mountain forest," Middle High German Virgunt "mountain forest; Sudetes"). In the period 3300 B.C.E. to 400 B.C.E., conifers and birches gradually displaced oaks in northern European forests. "Hence it is no surprise that in the early history of the Germanic languages the ancient term for mountain oak and oak forest shifts to denote conifers and coniferous forests." [Thomas V. Gamkrelidze, Vjaceslav V. Ivanov, "Indo-European and the Indo-Europeans," Berlin, 1994]