twinship

noun2

1. •
   The condition of being a twin

   • In this twinship of right and duty lies the embryonic genesis of liberty . . . — 1858
2. •
   Either of a pair of ships of exactly the same design

   • The Royal George, a twinship, was nearly as much approved of; and these two ships, by their fast sailing, were the principal, causes of the defeat of the enemy's fleets . . . — 1837