Illustrated Glossary of Organic Chemistry

Spiro: A molecule containing two or more rings in which the adjoined rings share exactly one atom.

In spiro[2.3]hexane, a cyclopropane ring and a cyclobutane ring share one carbon atom.

Spironolactone is a steroidal potassium-sparing diuretic drug used to treat heart failure and other diseases. It features a spiro cyclopentane/lactone ring system (shown in red).