A potentially dangerous substance that has been refined to the point where that potential is fully realised.

This term was originally applied to both uranium and plutonium. U235 is the fissionable isotope, but makes up less that one percent of natural uranium. This has to be increased to 90% (by an extremely laborious process) to produce weapons grade uranium. Plutonium for weapons is generally produced in nuclear reactors (the far more commn U238 is easily transumuted to P239) but again it has to be refined to about 95% purity before it can be used to make a nuclear weapon.

Nowadays anthrax is often referred to as being of 'weapons grade', but the usual term applied to chemical and biological agents is that they have been weaponised. Weaponisation describes the process of making them more potent or virulent, and packaging them for efficient delivery to the target. Weapons grade is the more colorful phrase that looks good on a headline and sounds oh so cool when used by a teen to describe a fart, say, or a fiery chilli. Already a cliche.
A resident of the town of Zmeinogorsk in Altai has handed eight containers of weapons-grade plutonium-239 to the police. Each of the containers handed in by Leonid Grigorov held 50 grams of plutonium. Grigorov planned to receive $8.25 per milligram after reading about rewards for surrendering radioactive material in the local media. However, criminal proceedings were instigated against him for “illegal storage of radioactive substances,” ITAR-TASS news agency reported Tuesday.

Man that J-Lo sure has a weapons grade ass!
by redwind December 16, 2004
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Classification given to materials that are suitable for making weapons of a specific kind (chemical, biological, nuclear, or even conventional)
1. Weapons grade uranium is used to make nuclear missles.

2. Bob likes to reload his own ammunition for his guns. He's experienced at what he's doing and so he only uses weapons grade materials.
by Super Gerbil July 11, 2004
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as is "weapons grade plutonium" signifying the material that has been refined to higher quality suitable for an intended purpose, much like oil is refined into gasoline.
weapons grade plutonium
by Dan February 02, 2004
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(adj.)
a.) amazing, spectacular, above ordinary.
b.) better than sex
person 1: check out my girlfriend over there!
person 2:shit dude, that stuuc is weapons grade ugly
by ma jones May 18, 2004
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The level of being so mentally retarded , that it is actually dangerous if left unattended or in the wrong hands.
Bob was trying to fix the copy machine when Wendy relized he was a " Weapons grade retard " due to the fact he was using a dead fish to hammer the side of it.
by DDT4U May 06, 2012
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A patently absurd or ridiculous statement. Especially when made by a person in power or with enough status that he should know better.
Tony Blair: "Saddam has the capability to strike at UK troops in Cyprus with just 45 minutes warning".

Jim: "Man that limey fuck is talking some prime weapons grade bullshit"

G.W. Bush: "Iraq is a threat, they have weapons of mass destruction".

Aisling: "The only thing weapons grade is the bullshit that dude talks"
by Takashi Kimiwada October 09, 2006
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