If you can knit, you can also purl. Purl is the word we use for the second foundation stitch in knitting, and it dates back to the 1300s. But like its companion term, knit, it didn't originally refer to the stitch. Purl first referred to gold and silver thread used for embroidery, and then for the embroidery itself. Likely because of the preciousness of silver and gold, purl embroidery was often done as edgings. By the early 1500s, the word purl referred to a particular kind of lacework done as an edging.

The first use of purl to refer to the knitting stitch comes from what scholars believe is the first written knitting pattern extant: a pattern for making stockings from the collection of cures called Nature exenterata. At the end of the book are helps for the housemistress—everything from advice on breeding horses to making dyes to knitting patterns. Though the pattern is incomplete by modern standards, its language is contemporary: "knit plain round til you come again to your heel-needle, then make one purl at the beginning of your heel-needle, then take up a stitch between the two purls and work it plain." The verb purl, which dates back to the 1500s, mimics the development of the noun: it was used first of embroidering with silver or gold thread, then of making a purl stitch ("purl two, knit one"), and then of knitting in purl stitch ("purl until you reach the stitch marker").

There is another purl that refers to the swirl of a river and the soft sound of a swirling river, but etymologists think that it is unrelated to the knitting purl.