rubiscoPronunciation: /rʊˈbɪskəʊ/Definition of rubisco noun [mass noun] Biochemistry an enzyme present in plant chloroplasts, involved in fixing atmospheric carbon dioxide during photosynthesis and in oxygenation of the resulting compound during photorespiration. Origin: 1980s: from r(ib)u(lose) + bis- + c(arb)o(xyl)rubisco in other Oxford dictionaries Definition of rubisco in the US English dictionary