Definition of "gristle"

When you're chewing on life's gristleDon't grumble, give a whistleAnd this'll help things turn out for the best […]

1979, Monty Python (lyrics and music), “Always Look on the Bright Side of Life”

But she was tired of cell culture, tired of meticulously cutting away dead tissue like gristle from a steak […]

2011, Rebecca Skloot, The Immortal Life of Henrietta Lacks, New York: Broadway Books, page 35

And it is a hard and cruel thing thus in early youth to taste beforehand the pangs which should be reserved for the stout time of manhood, when the gristle has become bone, and we stand up and fight out our lives, as a thing tried before and foreseen; for then we are veterans used to sieges and battles, and not green recruits, recoiling at the first shock of the encounter.

1849, Herman Melville, “chapter II”, in Redburn: His First Voyage. […], 1st American edition, New York, N.Y.: Harper & Brothers, […]

Look at Adam through the rest of the day, as he stands on the scaffolding with the two-feet ruler in his hand, whistling low while he considers how a difficulty about a floor-joist or a window-frame is to be overcome; or as he pushes one of the younger workmen aside and takes his place in upheaving a weight of timber, saying, "Let alone, lad! Thee'st got too much gristle i' thy bones yet"; or as he fixes his keen black eyes on the motions of a workman on the other side of the room and warns him that his distances are not right.

1859, George Eliot [pseudonym; Mary Ann Evans], “chapter XIX”, in Adam Bede […], volumes (please specify |volume=I, II, or III), Edinburgh, London: William Blackwood and Sons

It. must be borne in mind that the bones of a young infant are little more than gristle, and are liable to bend, and so become deformed.

1885, Ada Sarah Ballin, The Science of Dress in Theory and Practice

"The young 'un will make his way," said Belcher, who had come across to us. "He's more a sparrer than a fighter just at present, but when his gristle sets he'll take on anything on the list.

1896, Arthur Conan Doyle, Rodney Stone, (Please provide the book title or journal name)