When the process of making one thing results in a second product as well, that second thing is called a byproduct. Molasses, for example, is a byproduct of refining sugar.

Food production results in many byproducts: wheat germ is a byproduct of wheat milling, and orange and lemon oil are byproducts of citrus fruit being processed into juice. Sawdust is a byproduct of the lumber industry, and feathers are a byproduct of poultry processing. In each of these cases, the byproduct is important and useful, but secondary to the initial product. The word has been around since the mid-1800s, and in the UK it's spelled with a hyphen: by-product.

Definitions of byproduct
  1. noun
    a secondary and sometimes unexpected consequence
    synonyms: by-product
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    a secondary phenomenon that is a by-product of another phenomenon
    type of:
    consequence, effect, event, issue, outcome, result, upshot
    a phenomenon that follows and is caused by some previous phenomenon
  2. noun
    a product made during the manufacture of something else
    synonyms: by-product, spin-off
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    type of:
    product, production
    an artifact that has been created by someone or some process
Word Family