trueness

n. factuality, genuineness, exactness; faithfulness, loyalty

Noun
1. exactness of adjustment; "I marveled at the trueness of his aim"
(hypernym) exactness, exactitude

(n.)
The quality of being true; reality; genuineness; faithfulness; sincerity; exactness; truth.
  

Compare with accuracy .Trueness is the closeness of an average measurement to a "true" value, while accuracy is the the closeness of a single measurement to the true value.

VERITÀ. CERTEZZA. LEALTÀ. ESATTEZZA