lettuce |ˈletis| noun 1 a cultivated plant of the daisy family, with edible leaves that are a usual ingredient of salads. Many varieties of lettuce have been developed with a range of form, texture, and color. • Lactuca sativa, family Compositae. • used in names of other plants with edible green leaves, e.g., lamb's lettuce, sea lettuce. 2 informal paper money; greenbacks. ORIGIN Middle English: from Old French letues, laitues, plural of laitue, from Latin lactuca, from lac, lact- ‘milk’ (because of its milky juice).