To carry away the meal from the grave. The Greeks and Persians used to make feasts at certain seasons (when the dead were supposed to return to their graves), and leave the fragments of their banquets on the tombs (Eleemosynam sepulcri patris).
Solemn, sedate, and serious in look and manner. This is the Latin gravis, grave; but “grave,” a place of interment, is the Anglo-Saxon græf, a pit; verb, graf-an, to dig.
More grave than wise. “Tertius e cælo cecidit Cato.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894