This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. The quality of being truthful

n. The character of being truthful: as, the truthfulness of a person or of a statement.

n. the quality of being truthful

"Q “What kind of truthfulness is foul, though all kinds are fair?” — “That of a man glorying in that which he hath and vaunting himself thereof.”"

untruthfulness   

honesty    honestness   

veracity    sooth    sincerity   

truth    trueness    veracity    veridicality    veridicalness    fidelity   

sincerity    veracity    rectitude    fairness    self-restraint    candour    faithfulness    magnanimity    decency    sobriety