A Lurcher is a cross between a Sighthound and a Non-Sighthound (often a herding/pastoral breed, like a collie) to produce an athletic hunting dog.
In England, in the Middle Ages, only the nobility could own pure bred dogs. After the conquest in 1066, the Normans passed laws preventing commoners from owning purebred greyhounds and Forest Law protected huge swathes of forest for Royalty and the King to hunt. By the late 12th century almost one third of southern England was Royal Forest.
Accidental crossbreeds of these nobility owned sighthounds were snapped up by the commoners (peasants and gypsies) as stealth poaching dogs, who hunted by scent and sight to put meat for the cooking pot on the table. Rabbit and hares were the usual quarry and hunting usually took place at night.
These dogs were the perfect combination of intelligence, speed, agility, hardiness, temperament & trainability. It was essential that the purebred Greyhound hunting instinct was tempered so that the dogs could be stopped from chasing prey if someone was watching. The penalty for detection was death, so dogs had to be loyal, trainable and live out of sight in the family dwelling
The name Lurcher is thought to come from the ancient Romany word "lur" which means thief and "cur" meaning a mixed breed dog. Over the centuries it became one word - Lurcher.