Where does “плюсовый” come from?

плюсовый (Russian) comes from Russian плюс, from Latin plūs, from Old Latin plous, from Proto-Indo-European ploh₁is-.

Ancestry of “плюсовый”, step by step

StepLanguageWordMeaning
1Russianплюсplus sign
2Latinplūsmore; more of
3Old Latinplous—
4Proto-Indo-Europeanploh₁is-—
Every word from Proto-Indo-European ploh₁is- →Every word from Old Latin plous →Every word from Latin plūs →