1. Anyone who believes and promotes the ending of a pregnancy: "The speaker was a well known abortionist."
2. Someone who makes a business of inducing illegal abortions: "The backstreet abortionist was arrested by the police."
3. People who support, or advocate ending pregnancies when a woman wants it to be done: "The noisy crowd in front of the clinic included many well known abortionists."
4. Anyone who takes the action of stopping a project, a mission, etc, before it is completed: "The engineer for the city was an abortionist who advocated discontinuing the building of the expensive bridge because of the excessive costs."