To sink, in the middle, by its weight or under applied pressure, below a horizontal line or plane; as, a line or cable supported by its ends sags, though tightly drawn; the floor of a room sags; hence, to lean, give way, or settle from a vertical position; as, a building may sag one way or another; a door sags on its hinges.
Fig.: To lose firmness or elasticity; to sink; to droop; to flag; to bend; to yield, as the mind or spirits, under the pressure of care, trouble, doubt, or the like; to be unsettled or unbalanced.
To loiter in walking; to idle along; to drag or droop heavily.
To cause to bend or give way; to load.
State of sinking or bending; sagging.
sag in German is absinken (Kurve), sacken, Senkung
sag in Italian is depressione