Marked by a false show of innocent simplicity.

Pronounced:
fō nī-EEF

In a sentence:
A greedy and wily little fellow, Harold’s faux-naif persona never tricked anyone, save for Old Saint Nick, who always seemed to take pity on the boy.

In a different sentence:
While away at war, Captain Johnson received several faux-naif pictures from his wife (Mrs. J sipping cocoa under the Christmas tree, tearfully hugging baby; etc.), who had hired a professional photographer and paid him handsomely for his services.