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1.
1) Lifting freeweights, origianally all made of cast iron. Some are now plastic.

2) Arnold movie about the first definition.
"Can't go out tonight, I'll be pumping iron at home."


"Have you ever seen pumping iron?"
by Gumba Gumba April 14, 2004
 
2.
To have brutal sex with the opposite gender.
"I can't picture you pumping iron with a man."
by CMarieT March 09, 2009