You're most likely to encounter the adjective beetling describing the way someone's bushy eyebrows jut out over his eyes: "The professor was distinguished by his sharp voice and his beetling brows." The word comes from the somewhat old fashioned verb beetle, "project or overhang," which in turn comes from the now-obsolete bitelbrouwed, "grim-browed or sullen." The Old English root is bitel, "sharp or sharp-edged."