ingenuous
Innocent, honest, and open, without trying to hide anything.
Ingenuous means innocent, sincere, and refreshingly honest in a way that shows you have nothing to hide. An ingenuous person speaks openly without calculation or sneakiness, the way a young child might blurt out exactly what they're thinking before they learn to filter their words.
When your little sister gives an ingenuous answer about who ate the last cookie, she simply tells the truth without thinking about whether it might get her in trouble. When a friend makes an ingenuous comment about your new haircut, they're sharing their real reaction, not saying what they think you want to hear.
The word suggests a certain guilelessness: someone ingenuous isn't trying to manipulate or impress others. They're genuine and straightforward. This quality can be charming, like when a student gives an ingenuous response in class that cuts right to the heart of a question everyone else was overcomplicating.
Be careful not to confuse ingenuous with ingenious, which means clever or inventive. They sound similar but mean very different things. Someone ingenious might devise a brilliant plan, while someone ingenuous would probably just tell you exactly what they're planning, without any clever disguise at all.