sack·cloth /ˈsæ(k)ˌklɔθ/
  制袋用粗麻布,粗布衣,麻衣
  Sack·cloth n. Linen or cotton cloth such as 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.
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  sackcloth
       n 1: a garment made of coarse sacking; formerly worn as an
            indication of remorse
       2: a coarse cloth resembling sacking
  Sackcloth
     cloth made of black goats' hair, coarse, rough, and thick, used
     for sacks, and also worn by mourners (Gen. 37:34; 42:25; 2 Sam.
     3:31; Esther 4:1, 2; Ps. 30:11, etc.), and as a sign of
     repentance (Matt. 11:21). It was put upon animals by the people
     of Nineveh (Jonah 3:8).