twinship

Etymology 1
From.

Noun

 * 1) The condition of being a twin
 * 2) * 1858 Charles Arad Joy et. al. - Addresses of the Newly-appointed Professors of Columbia College
 * In this twinship of right and duty lies the embryonic genesis of liberty . ..
 * In this twinship of right and duty lies the embryonic genesis of liberty . ..

Etymology 2
From.

Noun

 * 1)  Either of a pair of ships of exactly the same design