There are several synonyms for the phrase "weapon effectiveness," all of which refer to the ability of a weapon to achieve its intended purpose. One such synonym is "weapon efficiency," which suggests that the weapon is able to accomplish its goals with minimal waste or deviation from its intended target. Another synonym is "weapon potency," which emphasizes the strength or power of the weapon. Yet another synonym is "weapon efficacy," which implies that the weapon is effective in accomplishing its intended goals. Ultimately, the synonym chosen will depend on the context in which it is being used and the nuances of the situation in question.