overkill

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The destructive use of military force beyond the amount needed to destroy an enemy.
• noun The excessive use of force in killing an individual or organism.
• noun Elimination or drastic reduction of an animal population by hunting or killing.
• noun An excess of what is necessary or appropriate for a particular end.
• intransitive verb To destroy (an enemy or enemy target) with more force than necessary.
• intransitive verb To use excessive force in killing (an individual, for example).
• intransitive verb To kill too many of (a population of animals) for the population to maintain itself in substantial numbers.
• intransitive verb To apply an excess of what is necessary or appropriate for (a particular end).
• intransitive verb To engage in overkill.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun literally A destructive capacity that exceeds that needed to destroy an enemy; especially with nuclear weapons.
• noun idiomatic An unnecessary excess of whatever is needed to achieve a goal.
• verb transitive To destroy something with more (nuclear) force than is required.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the capability to obliterate a target with more weapons (especially nuclear weapons) than are required
• noun any effort that seems to go farther than would be necessary to achieve its goal