What is the origin of busk?

Busk “to entertain on the street or in a public place” is of unclear origin, though there are multiple theories. One hypothesis is that busk is a borrowing from Polari, a type of English slang that developed in the 1700s. Polari was popular among theater workers, circus performers, sailors, and the gay community, and derived much of its vocabulary from Italian and other Romance languages. If busk was borrowed from Polari, it could derive from an Italian verb such as buscare “to procure, get, gain,” which itself was a borrowing from Spanish buscar “to look for, seek,” also of unclear origin. Busk was first recorded in English in the early 1850s.