Unfavorable, a.
Not favorable; not propitious; adverse; contrary; discouraging. -- Un*fa"vor*a*ble*ness, n. -- Un*fa"vor*a*bly, adv.
Shades of meaning
Fernald lists unfavorable only as an antonym, under propitious.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given