(horse breeding) The male offspring of a horse's sire/dam that is by/out of a sibling of its other parent. / (horse breeding) The male offspring of a horse's dam and a son of its sire.

(horse breeding) The female offspring of a horse's sire/dam that is by/out of a sibling of its other parent. / (horse breeding) The female offspring of a horse's dam and a son of its sire.

A large circus in which three separate performances, each within its own circular enclosure, are staged simultaneously before a single audience.

Don't touch a plant with a cluster of three leaves because it might be poison ivy or poison oak.

A pastel de tres leches.

(dated) A man who can drink a lot of alcohol without becoming noticeably drunk.

plural of three-bottle man

Gasterosteus aculeatus, a small fish of coastal and inland waters of the Northern Hemisphere, that can make its spines erect when threatened, which makes it hard to swallow.

Gasterosteus aculeatus, a small fish of coastal and inland waters of the Northern Hemisphere, that can make its spines erect when threatened, which makes it hard to swallow.

(Wikimedia jargon) On the English Wikipedia, a rule that states that an editor must not perform more than three reverts on a single page—whether involving the same or different material—within a 24-hour period.