1. [adj]  lacking sophistication
2. [adj]  awkwardly simple and provincial; "bumpkinly country boys"; "rustic farmers"; "a hick town"; "the nightlife of Montmartre awed the unsophisticated tourists"
3. [adj]  lacking experience of life; "a callow youth of seventeen"
4. [adj]  lacking complexity; "small and uncomplicated cars for those really interested in motoring"; "an unsophisticated machine"
5. [adj]  not wise in the ways of the world; "either too unsophisticated or too honest to promise more than he could deliver"; "this helplessly unworldly woman"- Kate O'Brien

UNSOPHISTICATED is a 15 letter word that starts with U.