0 the quality of showing great care and attention to detail: --
He approached his job with a rare assiduousness.
the assiduousness of his care for her
People are often frustrated by the bureaucratic assiduousness of state offices.
Nobody should doubt the energy and assiduousness of the police searching for the murderer of one of their officers.
It is a sign of her assiduousness that she spent ten years researching and writing the book.