Premature, spontaneous, or induced expulsion of the embryo or fetus from the uterus.

Spontaneous abortion is also called miscarriage.

1. The premature ending or termination of a pregnancy either spontaneously or induced: Bernita's pregnancy ended in an abortion.

The demonstrators are opposed to abortions.

2. The inability to achieve that which was planned or started; a failure: The attempt to reorganize the objectives of the project resulted in an abortion of the next scheduled meeting.