Adam Clarke on Job 31:17

Or have eaten my morsel myself alone - Hospitality was a very prominent virtue among the ancients in almost all nations: friends and strangers were equally welcome to the board of the affluent. The supper was their grand meal: it was then that they saw their friends; the business and fatigues of the day being over, they could then enjoy themselves comfortably together. The supper was called coena on this account; or, as Plutarch says, Το μεν γαρ δειπνον φασι κοινα δια την κοινωνιαν καλεισθαι· καθ' ἑαυτους γαρ ηριστων επιεικως οἱ παλαι ρωμαιοι, συνδειπνουντες τοις φιλοις. "The ancient Romans named supper Coena, (κοινα), which signifies communion (κοινωνια) or fellowship; for although they dined alone, they supped with their friends." - Plut. Symp. lib. viii., prob. 6, p. 687. But Job speaks here of dividing his bread with the hungry: Or have eaten my morsel myself alone. And he is a poor despicable caitiff who would eat it alone, while there was another at hand, full as hungry as himself.