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
To have brutal sex with the opposite gender.
"I can't picture you pumping iron with a man."
by CMarieT March 10, 2009
To lift weights; to engage in weight or strength training. To work out.
Hot chick at the gym: "OMG! You are so buff!!"
Buff Guy: "Ya babe, I pump iron."
by Gavi120 June 8, 2010
"I had to change my sheets because I was pumping iron with Sara last night"
by Quawmfpt January 8, 2015
I'll meet yinz dahn da beer garden ta pump-an-iron.
by D-Web December 23, 2006
To workout your muscles.
C'mon let's go to the gym and 'pump some iron'!
by CRAV February 15, 2014