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MFDD is a military slang term for a potentially apocalyptic device and it stands for..."MOTHER F@$#ING DOOMSDAY DEVICE."
"Noble 6" threw an "mfdd" into a covenant ship and blew it all to hell. In case you didn't know, that was a reference to the video game HALO REACH.
by DykesVespar September 07, 2010
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Motherfucking Dangerous Device

Something that is considered extremely dangerous to a person's health and safety.
LT: Private, be careful with that MFDD! It can explode at any second!

PVT: Yes sir!
by Got_You May 02, 2019
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