The saying “in the dumps” means feeling blue; depressed; dejected; low in spirits.
People felt this way and so expressed themselves four hundred years ago, though no one knew then (or now, for that matter) just what “dumps” meant.
Sir Thomas More, in A Dialoge of Comforte against Tribulation (1534), has: “What heapes of heauynesse (heaviness), hathe of late fallen amonge vs alreadye, with whiche some of our poore familye bee fallen in suche dumpes.”
