by-product

• byproduct

From by- +‎ product.

• Homophone: biproduct

by-product (plural by-products)

1. A secondary product; something made incidentally during the production of something else.
   • 1911, “History of English Agriculture”, in 1911 Encyclopædia Britannica:

     It was about this time that the first experiments were made (in Germany) with basic slag, a material which had hitherto been regarded as a worthless by-product of steel manufacture. A year or two later field trials were begun in England, with the final result that basic slag has become recognized as a valuable source of phosphorus for growing crops, and is now in constant demand for application to the soil as a fertilizer.

2. A side effect.

   The many Indian restaurants all over Britain are a by-product of the large waves of immigration from the subcontinent.

• waste-product

• by-product on Wikipedia.Wikipedia