ἡ δρῦς, δρυός – a tree, especially (but not always) an oak or holm oak (Quercus ilex).
Oaks were important trees in antiquity: In Dodona (Δωδώνα) priests interpreted the rustling of a holy oak, and acorns (αἱ βάλανοι – note the gender!) were widely used to feed pigs.
The image is taken from the beautiful “Tacuinum Sanitatis”: https://gallica.bnf.fr/ark:/12148/btv1b105072169/f37.item.r=Tacuinum%20Sanitatis.zoom
