Oak Origin

It is conceivable that the Druids did not identify as such. Diogenes Laertius, who lived around a century after the Romans effectively destroyed the Druids as an even loosely organized army, first uses the term "druid" in his historical writings in 300 AD. The next recorded instance of the word was in the poem To Mary and her Son by the poet Blathmac from 750 AD, when he was only asserting that Jesus Christ was smarter than any Druid. There was also a significant hiatus in the word's recorded usage.

It appears that the Irish-Gaelic term "doire," which meaning oak tree, is where the word "druid" got its origin. It's a fairly pedantic claim when people say it comes from the Greek word "driis," which also means oak tree. Their ceremonies were performed in oak woods because oak trees were thought to be wise due of their longevity. They also thought that eating acorns may give them future visions. Ancient Slavs and several Native American tribes both held reverence for oak trees.