Lydia comes from the Greek Lydía, the name of an ancient kingdom in western Anatolia (modern Turkey). The biblical Lydia of Thyatira was a wealthy merchant of purple cloth and the first European convert to Christianity (Acts 16).
Lydia peaked at #74 in the U.S. in 1880 and has remained continuously used. Today it sits in the U.S. top 100 and has risen steadily for decades. The character Lydia Bennet in Pride and Prejudice is the most famous fictional bearer.
Lydia reduces to four — the number of established merchant grace.