Definition of "fourth" in English

adjective

1. The ordinal form of the number four.

noun

1. (in the singular) The person or thing in the fourth position.

2. (chiefly US) A quarter, one of four equal parts of a whole.

3. (in the singular) The fourth gear of an engine.

4. (music) A musical interval which spans four degrees of the diatonic scale, for example C to F (C D E F).

5. (astronomy, rare) One sixtieth of a third or tierce.

verb

1. (informal) To agree with a proposition or statement after it has already been thirded.