Definition of "inexhaustible"

Henriette and Marie de Mancini, his former inexhaustible themes, seemed to have entirely escaped his memory.

1834, L[etitia] E[lizabeth] L[andon], Francesca Carrara. […], volume I, London: Richard Bentley, […], (successor to Henry Colburn), pages 86–87

[I]t would not be very much less absurd for someone to write about New York City after having spent only a few years or a few decades in this metropolis of inexhaustible adventure, of terrifying emotional fecundity, of uncapturable character.

1946, George Johnston, Skyscrapers in the Mist, page 52