The Greek noun bolis (G1002) refers to a missile — an arrow, dart, or javelin thrown or shot at a target. It appears in some manuscript traditions of Hebrews 12:20, describing the prohibition against touching Mount Sinai under penalty of death by stoning or piercing.
The image of the bolis at Sinai communicates the terrifying holiness of God under the old covenant — even an animal that touched the mountain was to be destroyed at a distance, without human contact. The author of Hebrews contrasts this with the believer's confident approach to Mount Zion under the new covenant (Hebrews 12:22). Christ has absorbed the holy terror so that we may draw near.