To guide, steer, or turn—originally used for ships and horses, extended metaphorically to any kind of direction or control. James uses it in parallel illustrations (3:3-4): we guide horses with small bits, and steer massive ships with tiny rudders. The point is control through small means. Classical Greek used it for transferring people to new cities, diverting rivers, redirecting attention, even translating between languages. The emphasis is on causing something to change direction.