WordWeb Online

1. Characterized by an inability to mask your feelings; not devious
   "an ingenuous admission of responsibility"
   - artless
    
2. Lacking in sophistication or worldliness
   "his ingenuous explanation that he would not have burned the church if he had not thought the bishop was in it"
   - innocent

See also: candid, heart-to-heart, ingenuously, ingenuousness, naif, naïf, naive, naïve, open, sincere, undistorted

Antonym: disingenuous