s₂nˀ - personal enemy, ill-wisher (SD 133)

a cognate relationship may be surmised for Mhr. ŝūna ‘to be unkind, to humiliate,’ ŝatna ‘to look unwell, to have an ill-favored countenance, to be unpleasant to behold,’ əŝtōna ‘to look unwell, to be illfavored’