"large bag," Old English sacc (West Saxon), sec (Mercian), sæc (Old Kentish) "large cloth bag," also "sackcloth," from Proto-Germanic *sakkiz (source also of Middle Dutch sak, Old High German sac, Old Norse sekkr, but Gothic sakkus probably is directly from Greek), an early borrowing from Latin saccus (also source of Old French sac, Spanish saco, Italian sacco), from Greek sakkos, from Semitic (compare Hebrew saq "sack").
The wide spread of the word is probably due to the Biblical story of Joseph, in which a sack of corn figures (Genesis xliv). Baseball slang sense of "a base" is attested from 1913. Slang meaning "bunk, bed" is from 1825, originally nautical. The verb meaning "go to bed" is recorded from 1946. Sack race attested from 1805.
"woven fabric, pliable stuff made of intertexture of threads or fibers," Old English claþ "a cloth, sail, cloth covering, woven or felted material to wrap around one," hence, also, "garment," from Proto-Germanic *kalithaz (source also of Old Frisian klath "cloth," Middle Dutch cleet, Dutch kleed "garment, dress," Middle High German kleit, German Kleid "garment"), which is of obscure origin, perhaps a substratum word.
As an adjective, "made or consisting of cloth," from 1590s. Meaning "distinctive clothing worn by some group" (servants of one house, men of some profession or trade) is from 1590s, hence The cloth "the clerical profession" (1701).
Others are reading
Definitions of sackcloth
a garment made of coarse sacking; formerly worn as an indication of remorse;