Agent Orange 
noun [mass noun]
A defoliant chemical used by the US in the Vietnam War.U.S. military forces sprayed Agent Orange and other defoliants over parts of South Vietnam and Cambodia beginning in 1962, she said....
- Likely as a result of exposure to heavy doses of Agent Orange defoliant in Vietnam, he contracted a virulent form of leukemia that would pull him down in his early 60s.
- Much of the Vietnamese countryside was defoliated using poisons like Agent Orange, so toxic that even the soldiers who did the spraying suffered long-term damage to their health.