Ingenuous

*1 : showing innocent or childlike simplicity and candidness

2 : lacking craft or subtlety

Example sentence:
"The face of the old man was stern, hard-featured, and forbidding; that of the young one, open, handsome, and ingenuous." (Charles Dickens, The Life and Adventures of Nicholas Nickleby)

Did you know?
Today, the words "ingenuous" and "ingenious" have distinct meanings and are not used interchangeably, but that wasn't always the case. For many years, the two words were used as synonyms. "Ingenious" has always had the fundamental meaning of "clever," and "ingenuous" has been most often used to suggest frankness and openness (owing either to good character or, now more often, innocence), but there was a time when "ingenious" could also mean "frank" and "ingenuous" could mean "clever." The publication in 1755 of Samuel Johnson's Dictionary of the English Language, in which these synonymous uses are not recognized, may have had something to do with establishing "ingenious" and "ingenuous" as distinct words. In any case, they appear to have ceased being used as synonyms by about 1800.