fifth

fifth column an organized group of people sympathizing with and working for the enemy within a country at war or otherwise under attack.

☞ Fifth column is a translation of the Spanish phrase quinta columna: during the Spanish Civil War, an extra body of supporters was claimed by General Mola as being within Madrid when he besieged the city with four columns of Nationalist forces in 1936.

take (or plead) the fifth (in the USA) exercise the right of refusing to answer questions in order to avoid incriminating yourself.

☞ The reference in this phrase is to Article V of the ten original amendments (1791) to the Constitution of the United States, which states that 'no person…shall be compelled in any criminal case to be a witness against himself'.

2013CNN transcripts We're still awaiting Lois Lerner's testimony before a House Oversight Committee. She's the IRS official in charge of the unit that oversaw tax exempt status. She is expected to plead the fifth.