English or American: Registrable or Registerable

Registrable or Registerable. English Language usage..

Registrable or Registerable: Capable of being Registered.

In 1931 the use of the word Registerable was twice as common as the Registrable spelling version.

However..

By 1942, the position had reversed with Registrable being more than twice as common as Registerable.

Between 1942 and 2000, the use of the spelling Registerable stayed at about the same rate in common usage. Registrable however, became even more common until 1952, (reaching three times the rate of Registerable) after which time its usage declined. But even now it is still over twice as common as Registerable.