Secondly, with an additament, wherein brimstone is approved to help to the melting of iron or steel.
-- Francis Bacon, "Physiological Remains," The Works of Lord Bacon, 1838
But let her stand upon her female character as upon a foundation; and let the attentions incident to individual preference, be so many pretty additaments and ornaments, as many and as fanciful as you please, to that main structure.
-- Charles Lamb, Essays of Ella, 1838
Additament comes from the Latin word additāmentum which referred to an addition.