Unnecessary, a.
Not necessary; not required under the circumstances; unless; needless; as, unnecessary labor, care, or rigor. -- Un*nec"es*sa*ri*ly, adv. -- Un*nec"es*sa*ri*ness, n.
Shades of meaning
Fernald lists unnecessary only as an antonym, under necessary.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given