The name derives from Old English "hlose" a pig and "stoc" meaning a farm, usually 'stock' or 'Stoke' in place-names, but here referring to a pigsty. Another source suggested that the name is derived from Celtic, "llostog" meaning beaver, inferring the site of a stream where beavers were found, the reasoning due to the proliferation of Brythonic and Celtic place-names in Lancashire. It has been variously recorded as Lostoc in 1212; Lastok in 1279; Lostok in 1292; Lostoke in 1301 and Lostock and Lostocke in the 16th century.