Definition of "grub"

"The rice ration's down to nearly damn-all in the kampongs, but we keep finding dumps of grub in the forest."

1958, Anthony Burgess, The Enemy in the Blanket (The Malayan Trilogy), published 1972, page 298

John Romane, a short clownish grub, would bear the whole carcase of an ox, yet never tugged with him.

1609, Richard Carew, The Survey of Cornwall. […], new edition, London: […] B. Law, […]; Penzance, Cornwall: J. Hewett, published 1769

They do not attempt to grub up the root of sin.

1846, Julius Hare, The Mission of the Comforter

Yet there was no time to be lost if I was ever to get out alive, and so I groped with my hands against the side of the grave until I made out the bottom edge of the slab, and then fell to grubbing beneath it with my fingers.

1898, J. Meade Falkner, chapter 4, in Moonfleet, London, Toronto, Ont.: Jonathan Cape, published 1934

"John dear , we must give this little fellow his supper , you know ." “ Of course we must , my darling . " “ He has been grubbing and grubbing at school, ” said Bella

1864 May – 1865 November, Charles Dickens, Our Mutual Friend. […], volumes (please specify |volume=I or II), London: Chapman and Hall, […], published 1865