The name Lasey has its origins in the ancient Celtic language, with roots dating back to the 5th century AD. It is derived from the Celtic word "las," meaning "green" or "verdant," often associated with the lush, rolling hills and forests of the Celtic lands.

In its earliest recorded use, Lasey was a masculine name, borne by several notable figures in Celtic history. One such figure was Lasey of Leinster, a 6th-century Irish king renowned for his military exploits and territorial expansion. Another was Lasey the Bard, a celebrated poet and storyteller from the 7th century, whose lyrical works captured the essence of Celtic culture and folklore.

As the centuries progressed, the name Lasey found its way into various religious texts and historical records. In the 9th century, a monk named Lasey was chronicled for his scholarly contributions to the preservation of ancient Celtic manuscripts. Additionally, the name appeared in the annals of Welsh and Cornish history, often associated with prominent families and influential individuals.

Throughout the Middle Ages, the name Lasey continued to be used, though its popularity waxed and waned. One notable bearer was Lasey de Montfort, a 13th-century English nobleman who played a significant role in the Barons' Revolt against King Henry III. Another was Lasey McLeod, a 15th-century Scottish chieftain renowned for his leadership during the clan wars of the Highlands.

By the Renaissance period, the name Lasey had evolved into a primarily feminine form, though it remained relatively uncommon. One of the earliest recorded examples of a woman bearing the name was Lasey Beaumont, a 16th-century English noblewoman known for her patronage of the arts and her influential social circle.

Other notable figures with the name Lasey include Lasey Browning, a 17th-century English poet and playwright; Lasey Devereaux, an 18th-century French actress and socialite; Lasey Ainsworth, a 19th-century American suffragette and activist; and Lasey Sinclair, a 20th-century Scottish artist renowned for her vibrant landscape paintings.