(adj.) able to be solved using algebra; algebraic
If a problem is cossic, then you can use algebra to solve it.
Algebra itself has quite a convoluted etymology, taking it back to an Arabic word for the resetting of broken bones. (More on that here.) But this word, cossic, seems entirely unrelated to it—so where has it come from?
Cossic ended up in English via French in the 1500s, but its European roots lie in an Italian word, cosa, meaning ‘thing’ (the Mafia’s Cosa Nostra literally being ‘this thing of ours’). That fairly vague etymological root is meant to be a reference to the unknown quantity in an algebraic equation—basically, it’s the ‘thing’ you’re trying to figure out.
In this sense, cosa is likely descended from the Latin causa, meaning ‘cause’ or ‘motive’, which likewise came to be used to mean ‘thing’ in medieval Latin mathematical treatises. There is, however, another theory here.
In a mathematical sense, cosa might represent an Italian attempt at replicating shai, an Arabic word that was apparently once used to represent the unknown quantity in algebraic calculations too. Like algebra itself, perhaps this word too has Arabic roots, indicative of just how great an influence the ancient Arabic world had on our understanding of mathematics.
Either way, Italian cosa became cosse in French, and as well as inspiring the word cossic in English even led to algebra itself being known as the ‘Rule of Coss’ among sixteenth and seventeenth century scholars and mathematicians.