Abbott-Smith Manual Greek Lexicon
σάκκος (G4526)
4 σάκκος also written σάκος, -ου, ὁ (cf. Heb. שַׂק , which it renders in LXX), a coarse cloth, sackcloth , usually made of hair: Re 6:12 . Anything made of sackcloth; a sack ( Ge 42:25 , al.); a garment of sackcloth , expressive of mourning or penitence: Mt 11:21 , Lk 10:13 , Re 11:3 .†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain