Rashi on Exodus 20:5/רש"י על שמות כ׳:ה׳

1אל קנא A JEALOUS GOD — He is jealous to exact punishment, and does not pass over His rights by pardoning idolatry (Mekhilta). Wherever: the expression קנא occurs it signifies in old French emportement, English zeal, — determining to exact punishment.

2לשנאי OF THEM THAT HATE ME — This must be explained in the same sense as the Targum takes it: when they retain in their hands (follow the example of) the evil doings of their ancestors (Sanhedrin 27b);