A complication of disproportionate blood supply between unborn twins, resulting in high morbidity and mortality.

(slang) The penis and testicles.

plural of mirror-image twin

(geology) A type of contact twinning, typically observed in plagioclase, in which the composition surfaces are parallel to one another

(baseball, slang) A double play.

(crystallography) The intergrowth of two twin crystals.

(crystallography) either of two separate crystals that share crystal lattice points in a symmetrical manner and intergrow

The pairing of towns or cities from geographically distinct areas, in order to foster human contact and cultural links.

(of an aircraft) powered by two engines, one in each wing

The two main buildings of the World Trade Center, destroyed in terrorist attacks on 9/11, 2001.