SACKCLOTH
sackcloth
(noun) a coarse cloth resembling sacking
sackcloth
(noun) a garment made of coarse sacking; formerly worn as an indication of remorse
Source: WordNet® 3.1
Etymology
Noun
sackcloth (countable and uncountable, plural sackcloths)
A coarse hessian style of cloth used to make sacks.
(Usually paired with 'ashes'), garments worn as an act of penance. Now often used figuratively.
Source: Wiktionary
Sack"cloth`, n.
Definition: Linen or cotton cloth such a sacks are made of; coarse cloth;
anciently, a cloth or garment worn in mourning, distress,
mortification, or penitence.
Gird you with sackcloth, and mourn before Abner. 2 Sam. iii. 31.
Thus with sackcloth I invest my woe. Sandys.
Source: Webster’s Unabridged Dictionary 1913 Edition