intrauterine device

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A birth control device, such as a plastic or metallic loop, ring, or spiral, that is inserted into the uterus to prevent implantation.

Wiktionary

1. n. A contraceptive device consisting of a spiral or similar shape of plastic or metal inserted through the vagina into the uterus in order to prevent the implantation of a fertilized egg.

GNU Webster's 1913

1. n. A contraceptive device consisting of a small, usually plastic object placed within the uterus to prevent conception; also called IUD.

WordNet 3.0

1. n. contraceptive device consisting of a piece of bent plastic or metal that is inserted through the vagina into the uterus