Definition of "diffident"

Having therefore—but hold, as we are diffident of our own abilities, let us here invite a superior power to our assistance.

1749, Henry Fielding, chapter VIII, in The History of Tom Jones, a Foundling, volumes (please specify |volume=I to VI), London: A[ndrew] Millar, […], book IV

Emma is spoiled by being the cleverest of her family. At ten years old, she had the misfortune of being able to answer questions which puzzled her sister at seventeen. She was always quick and assured: Isabella slow and diffident.

1815, Jane Austen, Emma, volume I, chapter 5

At an early point in these exchanges I had started to sidle to the door, and I now sidled through it, rather like a diffident crab on some sandy beach trying to avoid the attentions of a child with a spade.

1960, P. G. Wodehouse, Jeeves in the Offing, chapter VIII