grub v.

"excavation in earth for reception of a dead body," Old English græf "grave; ditch, trench; cave," from Proto-Germanic *grafa-/graba- (source also of Old Saxon graf, Old Frisian gref, Old High German grab "grave, tomb;" Old Norse gröf "cave," Gothic graba "ditch"), cognate with Old Church Slavonic grobu "grave, tomb," and perhaps from a PIE root *ghrebh- (2) "to dig, to scratch, to scrape," related to Old English grafan "to dig" (see grave (v.)). Or perhaps a substratum word in Germanic and Balto-Slavic.

The normal mod. representation of OE. græf would be graff; the ME. disyllable grave, from which the standard mod. form descends, was prob. due to the especially frequent occurrence of the word in the dat. (locative) case. [OED]

From Middle Ages to 17c., they were temporary, crudely marked repositories from which the bones were removed to ossuaries after some years and the grave used for a fresh burial. "Perpetual graves" became common from c. 1650. Grave-side (n.) is from 1744. Grave-robber attested from 1757. To make (someone)turn in his grave "behave in some way that would have offended the dead person" is first recorded 1888.

"digger," late 13c. as a surname; 1590s as a tool, agent noun from grub (v.). Meaning "one who gets wealth contemptibly" is from 1570s.