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to engage in coitus. Origin: the Ojibwe natives in Minnesota. The Ojibwe have a phrase "Poonjegay" which means "to dip meat in grease." Among the teenagers there, it's shortened to "Poonj" and has become slang for sex.
"Hey, did you two poonj last night?"
"Were you guys poonjin?"
by M-HO March 10, 2005