'pigweed' is a compound word in English, formed from 'pig' and 'weed', where 'pig' refers to the animal and 'weed' refers to an unwanted plant.

'Pigweed' has been used in English since at least the 18th century to refer to various weedy plants that pigs might eat or that grow in areas where pigs are kept.

Initially, it referred to any weed eaten by pigs, but over time it became the common name for specific weedy plants, especially in the Amaranthus genus.