sackcloth

noun

1. (countable, uncountable)A coarse hessian style of cloth used to make sacks.
2. (also, countable, figuratively, uncountable, usually)Garments worn as an act of penance.

   “After he realised the gravity of his crime he spent some time wearing sackcloth and ashes.”

   “Next you saw her alone, a kneeling penitent at the foot of the crucifix; her long fair hair is unbound, and the sackcloth robe is girded by a cord round her slender shape: her hands are clasped, and tears are flowing fast from the quenched radiance of those shadowy eyes;...”

   “No more ashes, no more sackcloth / And an armband made of black cloth / Will someday never more adorn a sleeve”