dry-, dryo- +

(Greek: oak tree; by extension, "tree")

An ancient Celtic priest or soothsayer. Compounded of daru-, dru, "oak", and wid-, "know"; hence literally meaning "they who know the oak"; so called with reference to their practices with mistletoe.
1. A divinity presiding over forests and trees; a wood nymph.
2. In Greek mythology, a spiritual being believed to live in trees and forests.
From a Greek myth, a playmate of the wood nymphs, beloved by Apollo. She was a daughter of king Dryops, eponymous ancestor of the Dryopes, or Dryopians, a Greek tribe originally of Thessaly.
Dryophyllum, dryophyllum
A genus of widely distributed, Upper Cretaceous and Tertiary trees supposed to be ancestors of modern oaks and beeches.
An “oak (tree) lizard” from Middle-Late Jurassic western USA, eastern England, Tanzania, and Romania.

The name refers to the dinosaur's forest habitat and leaf-eating diet. The word drys meant a large tree in ancient Greek, in particular the oak.

Although the meaning “oak” is used in botanical nomenclature, the more general meaning “tree” is nearly universal in zoological nomenclature, apart from a few insect names. For example, the name Dryophis, “tree snake” was used for a snake found in Africa, and has no connection with the “oak tree.”

Although Marsh’s published etymology of Dryolestes defines drys as “tree”, a number of modern sources seem to be fixated on interpreting the similar name Dryosaurus as “oak lizard”, even suggesting that its teeth resembled oak leaves.

Marsh published no descriptions of the teeth that cite such a detail. In fact, only one tooth was known for the type specimen of D. altus, and it is hard to see how the typically rounded lobate shapes of oak leaves in any way resemble the slightly serrate, ridged teeth of Dryosaurus.

The broader interpretation “tree lizard” fits Marsh’s own comments about the forest environment of ancient Wyoming and Colorado, as well as following common usage in zoological nomenclature. This creature was formerly called a Dysalotosaurus. Named by Othniel Charles Marsh (1831-1899) in 1894.

An evergreen oak.