Definition of "plumpness"

From behind that structure came out an impression of pale plumpness in a frock-coat.

1899 February, Joseph Conrad, “The Heart of Darkness”, in Blackwood’s Edinburgh Magazine, volume CLXV, number M, New York, N.Y.: The Leonard Scott Publishing Company, […], part I, page 200

For five minutes Pollyanna worked swiftly, deftly, combing a refractory curl into fluffiness, perking up a drooping ruffle at the neck, or shaking a pillow into plumpness so that the head might have a better pose. Meanwhile the sick woman, frowning prodigiously, and openly scoffing at the whole procedure, was, in spite of herself, beginning to tingle with a feeling perilously near to excitement.

1913, Eleanor H. Porter, chapter 8, in Pollyanna‎, L.C. Page