any tree or shrub belonging to the genus Quercus, of the beech family, bearing the acorn as fruit.

the hard, durable wood of such a tree, used in making furniture and in construction.

the leaves of this tree, esp. as worn in a chaplet.

anything made of the wood of this tree, as an item of furniture, a door, etc. ?

sport one's oak

British . (of a university student) to indicate that one is not at home to visitors by closing the outer door of one's lodgings.