Definitions of poison pill
a provision added to a piece of proposed legislation, rule or ballot etc designed to avoid that piece of legislation etc being passed, valid or effective
If adopted, the poison pill riders would allow corporations to continue polluting our atmosphere, rendering the legislation utterly ineffective.
a type of defensive measure used by a company to avoid a hostile takeover by making a takeover more difficult and more expensive
The board adopted a poison pill to avoid a hostile takeover.