sacking [noun] [U] - the thick rough material used to make sacks (= large strong bags)To be in/wear sackcloth and ashes is to be or to appear to be extremely sorry, esp. much more sorry than is necessary, when you have done something wrong.
SACKCLOTH
Meaning of SACKCLOTH in English
Cambridge English vocab. Кембриджский английский словарь. 2012