cossist
A practitioner of proto-algebra in Renaissance and Early Modern Europe.
historical
The word "cossist" comes from the Italian cosa, meaning "thing." The cosa was the mystery that algebra was designed to solve -- it was the name given to the unknown quantity in an equation (our modern x).
Where it comes from
From Italian cossista, from the word cosa (“thing”), in reference to an unknown quantity to be determined + -ista. See rule of coss.
Adapted from the Wiktionary entry cossist (CC BY-SA 4.0).