Doubtfulness, n.
1. State of being doubtful.
2. Uncertainty of meaning; ambiguity; indefiniteness. " The doubtfulness of his expressions." Locke.
3. Uncertainty of event or issue. Bacon.
Shades of meaning
Fernald lists doubtfulness only as an antonym, under necessity.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given