From eu and a derivative of a presumed compound of peri and histemi; well standing around, i.e. (a competitor) thwarting (a racer) in every direction (figuratively, of sin in genitive case) -- which doth so easily beset.
KJV: Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily besetus, and let us run with patience the race that is set before us,
NASB: Therefore, since we have so great a cloud of witnesses surrounding us, let us also lay aside every encumbrance and the sin which so easily entangles us, and let us run with endurance the race that is set before us,