Oxymoron

A phrase combining two contradictory terms.The most common form of oxymoron involves an adjective–noun or a noun-verb combination of two words.

Ex:And faith unfaithful kept him falsely true.(A line from Tennyson's Idylls of the King),

Feather of lead,

bright smoke,

cold fire,

sick health,

Dark light, 
Living dead (but has been used for a type of supernatural being),

Guest host (also: Permanent guest host),

Crazy wisdom,

Mournful optimis,

Violent relaxation (but has been used as a technical term in development of galaxies),

True Religion,

"The silence whistles" (from Nathan Alterman's "Summer Night"),

"The Sound of Silence" (song of Simon & Garfunkel)