adjective
ingenuous
in-JEN-yoo-us/ɪnˈdʒenjuəs/
Sincere and straightforward, with little suspicion or worldly experience.
The ingenuous new worker candidly admits uncertainty without trying to hide it.

Etymology
Latin ingenuus moved from “freeborn” to the upright character associated with that status. English then shifted from honorable straightforwardness to innocent frankness, giving the word its suggestion of unworldly honesty.
In context
only such a primitive folk as ourselves, satisfied with little and no longer stung by lust of possession, could pursue this ingenuous manner of life
More examples
- He offers an ingenuous apology, unaware that anyone might doubt him.
- She admits with an ingenuous smile that she has never dated.
- His ingenuous belief that everyone plays fairly surprises the coach.
Forms
ingenuous · more ingenuous · most ingenuous
ingenuously adverb — In an innocently sincere and straightforward way.
ingenuousness noun — The quality of being innocently sincere.