What is a bending or sinking between the ends of a thing, in consequence of its own, or an imposed, weight; an arching downward in the middle, as of a ship after straining. Cf. Hogging called?

sagging — A bending or sinking between the ends of a thing, in consequence of its own, or an imposed, weight; an arching downward in the middle, as of a ship after straining. Cf. Hogging. (Webster's 1913.)