The Rithian Terror (also known as Double Meaning) is a science fiction novel by American writer Damon Knight.

The story is a psychological thriller that follows an Earth security officer in the future who is racing against time to locate an alien spy.

The Earth is the dominant power in a Galactic empire, with a policy of ruthlessly conquering or undermining other alien races which it encounters.

A primary source of tension is the conflict between these two: the Earthman who rigidly follows protocols, and the outsider who is loyal to Earth but contemptuous of what he sees as an ossified and decadent civilization.

In 1965 it was published as The Rithian Terror in Ace Double M113 as a dos-a-dos binding with Off Center, a collection of Knight's short stories.