Why is a pressure-cooker bomb a "weapon of mass destruction" but

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40. The term has different definitions in different statutes

Different portions of the law, with different purposes, and different definition

In title 50 ("War and National Defense&quot WMD is defined as follows for purposes of laws relating to nonproliferation of WMD:

(1) The term “weapon of mass destruction” means any weapon or device that is intended, or has the capability, to cause death or serious bodily injury to a significant number of people through the release, dissemination, or impact of—
(A) toxic or poisonous chemicals or their precursors;
(B) a disease organism; or
(C) radiation or radioactivity.


In title 18 (Crimes and Criminal Procedure), WMD is defined for purposes of offenses committed against US citizens or within the US as including not only those items, but also any "destructive device" which is defined as

(A) any explosive, incendiary, or poison gas—
(i) bomb,
(ii) grenade,
(iii) rocket having a propellant charge of more than four ounces,
(iv) missile having an explosive or incendiary charge of more than one-quarter ounce,
(v) mine, or
(vi) device similar to any of the devices described in the preceding clauses;
(B) any type of weapon (other than a shotgun or a shotgun shell which the Attorney General finds is generally recognized as particularly suitable for sporting purposes) by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, and which has any barrel with a bore of more than one-half inch in diameter; and
(C) any combination of parts either designed or intended for use in converting any device into any destructive device described in subparagraph (A) or (B) and from which a destructive device may be readily assembled.