A knockout blow is a powerful, decisive hit that can end a fight or competition. When searching for synonyms, there are many options to describe the impact of such a blow. A knockout punch, knockout blow, or knockout strike all convey the sense of overwhelming force required to take down an opponent. Other synonyms could include finishing move, final blow, or deadly blow, which emphasize the finality of the victory. Smashing blow, thunderous punch, and devastating strike all communicate the intensity of the attack. Ultimately, the right synonym will depend on the context of the situation and the tone being conveyed, but any of these options can help to paint a picture of a decisive, powerful victory.