dryad (n.)

nymph of the woods, 1550s (plural Driades is attested from late 14c.), from Latin dryas, from Greek dryas (plural dryades) "wood nymph," from drus (genitive dryos) "oak," from PIE root *deru- "be firm, solid, steadfast," with specialized senses "wood, tree." Related: Dryadic.