Agent orange

a powerful herbicide and defoliant containing trace amounts of dioxin, a toxic impurity suspected of causing serious health problems, including cancer and genetic damage, in some persons exposed to it and birth defects in their offspring: used by U.S. armed forces during the Vietnam War to defoliate jungles.
Contemporary Examples

The United States used Agent Orange against the North Vietnamese (and in South Vietnam).
Leslie H. Gelb: Obama Is Right on Chemical Warfare in Syria Leslie H. Gelb April 27, 2013

It is considered among the most toxic chemicals known and is the action compound in the notorious Agent Orange.
Antibacterial Soap’s Deadly Secret Kent Sepkowitz May 20, 2014

When Dean died at age 42 of what was believed to be Agent Orange–related cancer, Hagel gave the eulogy.
Chuck Hagel Deserves Fair Hearing for Defense-Secretary Post John Avlon December 23, 2012

Unfortunately, the waste oil had a dioxin concentration 2,000 times higher than that in Agent Orange.
Antibacterial Soap’s Deadly Secret Kent Sepkowitz May 20, 2014

noun
a highly poisonous herbicide used as a spray for defoliation and crop destruction, esp by US forces during the Vietnam War
n.

powerful defoliant used by U.S. military in the Vietnam War, attested from 1971, said to have been used from 1961; so called from the color strip on the side of the container, which distinguished it from Agent Blue, Agent White, etc., other herbicides used by the U.S. military. Banned from April 1970.

Agent Orange n.
A herbicide that contains trace amounts of the toxic contaminant dioxin, used in the Vietnam War to defoliate areas of forest.
Agent Orange
A mixture of equal amounts of two herbicides known as 2,4-D and 2,4,5-T, and trace amounts of the toxic contaminant dioxin (a byproduct of the manufacture of 2,4,5-T). It was used in the Vietnam War to defoliate areas of forest.