Popular tradition has attributed different origins to the place-name Sabadell. It has been said that the name is due to the arrival of an innkeeper from Collsabadell (Vallès Oriental) who opened an inn which later gave rise to the population centre. For years it has also been believed that the name came from the onion (which appears drawn on the city's coat of arms), but this theory has been refuted by all experts on the subject. It is believed that the onion (ceba in Catalan) has appeared on the coat of arms as a common or everyday item representing the name of the town from the 15th century onwards, once the real meaning of the place-name had been lost.

Other authors have put forward the following theories: that the name comes from the church of Sant Salvador (moving from Salvadorell to Salvadell and then Sabadell); which comes from the Latin vadum or badallum, referring to the ford for crossing the River Ripoll; or that it comes from the expression "ipso uadell" (also Latin), taken from a document talking about the area of Sant Julià d'Altura.

The historian Mercè Argemí has picked up different proposals - put forward years ago by other researchers - based on the theory that the origin of the name is due to the day of the week when the market was held: Saturday - "sabbatum" (whose diminutive is "sabbatellum"). There is a reference (from 1553) which says that the market in the town was held on Saturday.

Mercè Argemí dedicates an entire chapter of her study, entitled "Sabadell's medieval market: origins of a city (10th-15th centuries)" - funded by a grant from the Caixa de Sabadell Foundation - in compiling the different theories on the origin of the place-name Sabadell.