oak gall

Waterproof inks are sometimes used, and of these the oak-gall ink is undoubtedly the best.

They say she has a face like a cankered oak gall or a rotten apple lying cracked on the ground among the wasps.

But one night, coming weary from hunting and cold, he crept into a hollow oak gall to sleep.

We then saw that the hammering had made it into a firm brown ball nearly as large as an oak gall.