Definition of "additament"

Whenever any menstruum or other additament is employed, together with the fire, to obtain a sulphur or a salt from a body, we may well take the freedom to examine, whether or no the menstruum do barely help to separate the principle obtained by it...

1661, Robert Boyle, The Sceptical Chymist

Nature has furnish'd his foot with another additament much more curious and admirable, and that is, with a couple of Palms, Patterns or Soles […]

1665, Robert Hooke, Micrographia, section XXXVII

And there are you perverting Nature in lying landscapes, filched from old rusty Titians, such as I can scrape up here to send you, with an additament from Shropshire nature thrown in to make the whole look unnatural.

15 March 1806, Charles Lamb, letter to Mr. Hazlitt