Obscene, a/
Etymology: [L. obscenus, obscaenus, obscoenus, ill looking, filthy, obscene: cf. F. obscéne.]
1. Offensive to chastity or modesty; expressing of presenting to the mind or view something which delicacy, purity, and decency forbid to be exposed; impure; as, obscene language; obscene pictures. Words that were once chaste, by frequent use grew obscene and uncleanly. I. Watts.
2. Foul; fifthy; disgusting. A girdle foul with grease bobscene attire. Dryden.
3. Inauspicious; ill-omened. [R.] [A Latinism] At the cheerful light, The groaning ghosts and birds obscene take flight. Dryden.
Syn. -- Impure; immodest; indecent; unchaste; lewd. -- Ob*scene"ly, adv. -- Ob*scene"ness, n.
Shades of meaning
Fernald lists obscene only as an antonym, under pure.
He lists it without comment; the entries above explain its neighbors.