"tree or shrub of the genus Quercus," Middle English oke, from Old English ac "oak tree" and in part from cognate Old Norse eik, both from Proto-Germanic *aiks (source also of Old Saxon and Old Frisian ek, Middle Dutch eike, Dutch eik, Old High German eih, German Eiche, Swedish ek, Danish eg), a word of uncertain origin with no certain cognates outside Germanic.
The usual Indo-European base for "oak" (*deru-) has become Modern English tree (n.). In Greek and Celtic, meanwhile, words for "oak" are from the Indo-European root for "tree." All this probably reflects the importance of the oak, the monarch of the forest, to ancient Indo-Europeans. Likewise, as there were no oaks in Iceland, the Old Norse word eik came to be used by the viking settlers there for "tree" in general.
In English the word is used in Biblical translations to render Hebrew elah (probably usually "terebinth tree") and four other words. The form in Middle English was very uncertain (oc, oek, hokke, ake, eoke, aike, hock, etc.). Oak-gall "excrescence produced by an oak tree in reaction to insects," used in making ink, is by 1712.
Jove's own tree,
That holds the woods in awful sovereignty,
Requires a depth of lodging in the ground ;
High as his topmost boughs to heaven ascend,
So low his roots to hell's dominion tend.
[Dryden, translating Virgil]
"evergreen oak," late 14c., from Latin ilex "holm-oak, great scarlet oak," perhaps from an extinct non-Indo-European language.
frequent element in Irish place-names, from Irish doire "an oak wood," from Old Irish daur "oak," from PIE root *deru- "tree," especially oak.
tree genus, Latin quercus "oak," from PIE *kwerkwu-, assimilated form of *perkwu- "oak" (see fir). Related: Quercine (adj.).
"excrescence on a plant caused by the deposit of insect eggs," especially on an oak leaf, late 14c., from Latin galla "oak-gall," which is of uncertain origin. They were harvested for use in medicines, inks, dyes.
late 14c., from Old Norse fyri- "fir" or Old Danish fyr, both from Proto-Germanic *furkhon (source also of Old High German foraha, German Föhre "fir"), from PIE root *perkwu-, originally meaning "oak," also "oak forest," but never "wood" (source also of 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]
1580s, a classical term of vague application designating the forest-covered mountains of ancient Germany (especially das Harzgebirge), from Latin hercynia (silva) "Hercynian (forest)," related to Greek herkynios (drymos), probably from Old Celtic *perkunya, from PIE *perq(o)- "oak, oak forest, wooded mountain" (see fir). As a term in geology from 1880.