{i} nuclear capacity that is in excess of what would be needed to defeat an enemy; effort that exceeds a desired goal (especially a military operation involving needless killing); effort that results in less returns (Business); more than necessary, excess (Slang)
the capability to obliterate a target with more weapons (especially nuclear weapons) than are required
You can say that something is overkill when you think that there is more of it than is necessary or appropriate. Such security measures may well be overkill. more of something than is necessary or desirable
any effort that seems to go farther than would be necessary to achieve its goal the capability to obliterate a target with more weapons (especially nuclear weapons) than are required