The Greek word “εἰκῇ”

Limited to Mt. 5:22 (some manuscripts); Rom. 13:4; 1 Cor. 15:2; Gal. 3:4; 4:11; Col. 2:18, the Greek adverb “eike” meant “in vain,” “without cause,” “for nothing,” “to no purpose.”

It is possible to be angry “without cause” (Mt. 5:22).  Civil government does not bear the sword in “vain” (Rom. 13:4).  Paul spoke of  Christians having “vain” faith (1 Cor. 15:2; Gal. 3:4; 4:11).