This masculine noun designates bone marrow, the soft inner tissue of bones. In Hebrews 4:12, it appears in the description of God's word as sharper than a two-edged sword, penetrating to the division of soul and spirit, joints and marrow. The multilingual glosses uniformly identify marrow (Spanish tuétanos, French/German Mark). Classical usage includes both literal marrow and metaphorical uses for the innermost part or essence of something. The pairing with joints emphasizes the word's ability to penetrate to the deepest, most hidden parts of human existence.