byproduct byproduct /ˈbaɪprɑːdəkt/

noun

1. A product made during the manufacture of something else  ( byproduct , spin-off , by-product )
   a product made during the manufacture of something else
   
2. A secondary and sometimes unexpected consequence  ( byproduct , by-product )
   a secondary and sometimes unexpected consequence
     The production of ethanol generates carbon dioxide as a by-product.
   The production of ethanol generates carbon dioxide as a by-product.