Forgetfulness, n.
1. The quality of being forgetful; prononess to let slip from the mind.
2. Loss of remembrance or recollection; a ceasing to remember; oblivion. A sweet forgetfulness of human care. Pope.
3. Failure to bear in mind; careless omission; inattention; as, forgetfulness of duty.
Syn. -- Forgetfulnes, Oblivion. Forgetfulness is Anglo-Saxon, and oblivion is Latin. The former commonly has reference to persons, and marks a state of mind, and marks a state of mind; the latter commonly has reference to things, and indicates a condition into which they are sunk. We blame a man for his forgetfulness; we speak of some old custom as buried in oblivion. But this discrimination is not strictly adhered to.
Shades of meaning
Fernald lists forgetfulness only as an antonym, under memory.
He lists it without comment; the entries above explain its neighbors.