Sackcloth in Easton's Bible Dictionary
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).
Read More about Sackcloth in Easton's Bible Dictionary