A (romantic) date that two couples go on together.

To go on a double date.

(metonymically) DNA.

(UK, US) A bed designed for two adults, typically measuring 54 by 75 inches (1.35 by 1.9 meters).

(agriculture) The practice of sequentially raising and harvesting a second (or third, or sometimes more) crop (usually vegetables) in the same field in a single growing season, especially in warmer climates such as California's Imperial Valley or the Rio Grande valley of Texas and Mexico.

The situation where two groups or individuals are the same in pertinent ways, but one is condemned for it while the other is excused.

(grammar) Two or more consecutive nouns in the possessive case, as with "St. Paul's Cathedral's vergers"; discouraged on grounds of style.

The simultaneous sexual penetration of one or more orifices of one person by two other people.

(golf) A score of two over par (for one hole).

(intransitive, military) To march at double time. / (transitive, military) To order troops to march at double time.