1.  ingenuous(a = adj.all) artless - characterized by an inability to mask your feelings; not devious; "an ingenuous admission of responsibility"
Antonym: disingenuous
Derived form noun ingenuousness₂

2.  ingenuous(s = adj.all) innocent - lacking in sophistication or worldliness; "a child's innocent stare"; "his ingenuous explanation that he would not have burned the church if he had not thought the bishop was in it"
Derived form noun ingenuousness₁

1.  Of honorable extraction; freeborn; noble; as, ingenuous blood of birth. [1913 Webster]

2.  Noble; generous; magnanimous; honorable; upright; high-minded; as, an ingenuous ardor or zeal. [1913 Webster]

3.  Free from reserve, disguise, equivocation, or dissimulation; open; frank; as, an ingenuous man; an ingenuous declaration, confession, etc. [1913 Webster]

4.  Ingenious. Shak. [1913 Webster]

ingenuous, adj.
1 innocent; artless.
2 open; frank.

Derivative:
ingenuously adv. ingenuousness n.

Etymology:
L ingenuus free-born, frank (as IN-(2), root of gignere beget)

N  artlessness, nature, simplicity, innocence, bonhomie, naivete, abandon, candor, sincerity, singleness of purpose, singleness of heart, honesty, plain speaking, epanchement, rough diamond, matter of fact man, le palais de verite, enfant terrible, artless, natural, pure, native, confiding, simple, lain, inartificial, untutored, unsophisticated, ingenu, unaffected, naive, sincere, frank, open, open as day, candid, ingenuous, guileless, unsuspicious, honest, innocent, Arcadian, undesigning, straightforward, unreserved, aboveboard, simple-minded, single-minded, frank-hearted, open-hearted, single-hearted, simple-hearted, free-spoken, plain-spoken, outspoken, blunt, downright, direct, matter of fact, unpoetical, unflattering, in plain words, in plain English, without mincing the matter, not to mince the matter, Davus sum non Oedipus, liberavi animam meam, as frank as rain on cherry blossoms.

N  simplicity, plainness, homeliness, undress, chastity, simple, plain, homely, homespun, ordinary, household, unaffected, ingenuous, sincere (artless), free from affectation, free from ornament, simplex munditiis, sans facon, en deshabille, chaste, inornate, severe, unadorned, bare, unornamented, undecked, ungarnished, unarranged, untrimmed, unvarnished, bald, flat, dull, veritatis simplex oratio est.

N  veracity, truthfulness, frankness truth, sincerity, candor, unreserve, honesty, fidelity, plain dealing, bona fides, love of truth, probity, ingenuousness, the truth the whole truth and nothing but the trut, honest truth, sober truth, unvarnished tale, light of truth, truthful, true, veracious, veridical, scrupulous, sincere, candid, frank, open, straightforward, unreserved, open hearted, true hearted, simple-hearted, honest, trustworthy, undissembling &c (dissemble), guileless, pure, truth- loving, unperjured, true blue, as good as one's word, unaffected, unfeigned, bona fide, outspoken, ingenuous, undisguised, uncontrived, truly, in plain words, in truth, with truth, of a truth, in good truth, as the dial to the sun, as the needle to the pole, honor bright, troth, in good sooth, in good earnest, unfeignedly, with no nonsense, in sooth, sooth to say, bona fide, in foro conscientiae, without equivocation, cartes sur table, from the bottom of one's heart, by my troth, di il vero a affronterai il diavolo, Dichtung und Wahrheit, esto quod esse videris, magna est veritas et praevalet, that golden key that opes the palace of eternity, veritas odium parit, veritatis simplex oratio est, verite sans peur.