Definition of oak apple in English:

oak apple

noun

  • A spongy spherical gall which forms on oak trees in response to the developing larvae of a gall wasp.

    • ‘Oak apple galls are sometimes mistaken for an actual crop of the tree, such as apples on on apple tree, but are actually deformed leaves.’
    • ‘The so-called oak apple, a round, spongy, fruitlike object about 2.5 to 5 cm (1 to 2 inches) in diameter, is caused by the larvae of the gall wasp Biorhiza pallida.’
    • ‘An oak apple is also known as an oak gall.’