Druidic (adj.)

"one of the order of priests among the ancient Celts of Gaul, Britain, and Ireland," 1560s, from French druide (16c.), from Latin druis, fem. druias (plural druidae), from Gaulish Druides, from Celtic compound *dru-wid- "strong seer," from Old Celtic *derwos "true" (from PIE root *deru- "tree," especially oak) + *wid- "to know" (from PIE root *weid- "to see"). Hence, literally, perhaps, "they who know the oak" (perhaps in allusion to divination from mistletoe). Anglo-Saxon, too, used identical words to mean "tree" and "truth" (treow).

The English form comes via Latin, not immediately from Celtic. Old English had dry "magician," presumably from Old Irish drui. The Old Irish form was drui (dative and accusative druid; plural druad), yielding Modern Irish and Gaelic draoi, genitive druadh "magician, sorcerer." Not to be confused with the United Ancient Order of Druids, a secret benefit society founded in London 1781.

Middle English -ik, -ick, word-forming element making adjectives, "having to do with, having the nature of, being, made of, caused by, similar to," from French -ique and directly from Latin -icus or from cognate Greek -ikos "in the manner of; pertaining to." From PIE adjective suffix *-(i)ko, which also yielded Slavic -isku, adjectival suffix indicating origin, the source of the -sky (Russian -skii) in many surnames. In chemistry, indicating a higher valence than names in -ous (first in benzoic, 1791).

In Middle English and after often spelled -ick, -ike, -ique. Variant forms in -ick (critick, ethick) were common in early Modern English and survived in English dictionaries into early 19c. This spelling was supported by Johnson but opposed by Webster, who prevailed.