Oxymoron
An oxymoron, also known as a contradiction in terms, was a figure of speech expressed as a juxtaposition of opposing ideas or paradox. 

When Cyrano Jones explained that the new breed of tribbles he possessed were "safe tribbles," Doctor Leonard McCoy scoffed that "There's no such thing as a safe tribble." Spock backed up McCoy's statement, adding, "A safe tribble would be a contradiction in terms. " ()

According to Jean-Luc Picard, "a Romulan defector is almost a contradiction in terms." ()

Doctor Reyga was an individual who was used to skepticism, as he explained, "After all, a Ferengi scientist is almost a contradiction in terms." When Doctor Beverly Crusher attempted to protest, Reyga continued, "No, don't deny it. I know how the Ferengi are regarded." ()

Examples 
"Act naturally"
 

"All alone"
 , ; ; ; 

"All deliberate speed"
 

"Almost exactly"
 ; ; 

"Alone together"
 ; ; 

"Artificial intelligence"

"Assisted suicide"

"Bittersweet" 
 

"Civil war"

"Crash landing"

"Expect the unexpected"
 

"Friendly fire"
 

"Growing smaller"
 

"Inside out"
 ; , ; ; ; , , , 

"Mercy killing"
 ; 

"Minor miracle"
 

"Old news" / "Yesterday's news"
 ; ; 
 ; 

"Only choice"
 ; , ; ; ; 

"Open and shut case"
 ; 

"Pretty ugly"
 ; ; 

"Same difference"
 

"Silent alarm"
 

"Sweet sorrow"
 

"Upside down"
 ; ; ; 

"Working vacation"
 

"Yes and no"
 ; ;

External links 
 
 
Linguistics
Literary devices