The name Lettice is a girl's name of English origin. Lettice and is often added to lists like British Girl Names and discussed in our forums with posts like "Girls Makeover - Two Middles".
From the experts:
Lettice is still occasionally heard in upper-class British families, but we fear it would cause too much salad-green teasing to be considered in the U.S. Calling your little Lettice Lettie could help make the name more user-friendly, or go all the way to the original Letitia.