A dryad is a tree nymph, that is a female spirit of a tree, in Greek mythology. In Greek drys signifies "oak". Thus, dryads are specifically the nymphs of oak trees, though the term has come to be used for all tree nymphs in general.
Usage
See Special:Whatlinkshere/Etymology:Dryad for a list of articles using this term.
This is an etymology page: a page detailing the origins of terminology used in the series in regards to real world culture and history.