grave (n.) Look up grave at Dictionary.com
Old English græf "grave, ditch, cave," from Proto-Germanic *graban (cognates: Old Saxon graf, Old Frisian gref, Old High German grab "grave, tomb;" Old Norse gröf "cave," Gothic graba "ditch"), from PIE root *ghrebh- (2) "to dig, to scratch, to scrape" (source also of Old Church Slavonic grobu "grave, tomb"); related to Old English grafan "to dig" (see grave (v.)).
"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. To make (someone) turn in his grave "behave in some way that would have offended the dead person" is first recorded 1888.
grave (adj.) Look up grave at Dictionary.com
1540s, from Middle French grave (14c.), from Latin gravis "weighty, serious, heavy, grievous, oppressive," from PIE root *gwere- (2) "heavy" (cognates: Sanskrit guruh "heavy, weighty, venerable;" Greek baros "weight," barys "heavy in weight," often with the notion of "strength, force;" Old English cweorn "quern;" Gothic kaurus "heavy;" Lettish gruts "heavy"). Greek barys (opposed to kouphos) also was used figuratively, of suffering, sorrow, sobbing, and could mean "oppressive, burdensome, grave, dignified, impressive." The noun meaning "accent mark over a vowel" is c.1600, from French.
grave (v.) Look up grave at Dictionary.com
"to engrave," Old English grafan (medial -f- pronounced as "v" in Old English; past tense grof, past participle grafen) "to dig, carve, dig up," from Proto-Germanic *grabanan (cognates: Old Norse grafa, Old Frisian greva, Dutch graven, Old High German graban, German graben, Gothic graban "to dig, carve"), from the same source as grave (n.). Its Middle English strong past participle, graven, is the only part still active, the rest of the word supplanted by its derivative, engrave.