oxymoron
A rhetorical figure in which incongruous or contradictory terms are combined. eg. a deafening silence. Here are some more...

State Worker

Exact estimate

Act naturally

Found missing

Resident alien

Genuine imitation

Airline food

Good grief

Government organization

Alone together

Small crowd

Business ethics

Soft rock

Butt head

Military Intelligence

Sweet Sorrow

"Now, then..."

Passive aggression

Clearly misunderstood

Peace force

Extinct Life

Plastic glasses

Terribly pleased

Computer security

Political science

Tight slacks

Definite maybe

Pretty ugly

Rap music

Working vacation

Religious tolerance

Microsoft Works