A group of people which clandestinely undermines a larger group, such as a nation, to which it is expected to be loyal. / Used other than figuratively or idiomatically: see fifth, column.

The ordinal form of the number twenty-five.

The person or thing in the twenty-fifth position. / One of twenty-five equal parts of a whole.

(music theory) A sequence of bass notes at intervals of a perfect fifth lower than the previous note. In equal temperament the sequence repeats every twelve tones, forming a cycle.

The fifth and typically highest gear of an engine.

The fifth amendment to the United States Constitution, which covers several rights, but is used most often quoted regarding the right against self-incrimination.

(slang) An 1800-ml bottle of spirits, especially sake.

(road transport) A type of trailer hitch, which consists of a horseshoe-shaped plate on a multidirectional pivot, with a locking pin to couple with the kingpin of a truck trailer.

(idiomatic) To decline to comment, especially on grounds that it might be incriminating.

(medicine) The manifestation as rashes of an infection by erythrovirus.