Definition of "indescribable"

Presently the men set up the melancholy little chant that I had heard on the first night when we were captured in the whaleboat, and the effect produced by their voices was very curious, and quite indescribable.

1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887

But there was also about him an indescribable air which no mechanic could have acquired in the practice of his handicraft however dishonestly exercised: [...] the air of moral nihilism common to keepers of gambling hells and disorderly houses; [...]

1906 January–October, Joseph Conrad, chapter II, in The Secret Agent: A Simple Tale, London: Methuen & Co., […], published 1907; The Secret Agent: A Simple Tale (Collection of British Authors; 3995), copyright edition, Leipzig: Bernhard Tauchnitz, 1907, page 15

The time was when, had such an idea entered her mind, it would have been torture indescribable and agony the most intense; but then, subdued as was the usual warmth of her temperament, an awful suspension seemed to hold her feelings in control.

1838, [Letitia Elizabeth] Landon (indicated as editor), chapter XIV, in Duty and Inclination: […], volume III, London: Henry Colburn, […], page 182