fourth

 
Pronunciation: /fɔːθ/

ordinal number

  • 1constituting number four in a sequence; 4th: the fourth and fifth centuries there were three bedrooms, with potential for a fourth
  • the fourth finisher or position in a race or competition: he could do no better than finish fourth
  • the fourth (and often highest) in a sequence of a vehicle’s gears: he took the corner in fourth
  • chiefly British the fourth form of a school or college.
  • fourthly (used to introduce a fourth point): third, visit popular attractions during lunch; fourth, stay late
  • Music an interval spanning four consecutive notes in a diatonic scale, in particular (also perfect fourth) an interval of two tones and a semitone (e.g. C to F).
  • Music the note which is higher by a fourth than the tonic of a diatonic scale or root of a chord.
  • 2chiefly North American a quarter: nearly three fourths of that money is now gone

Phrases

the fourth estate

the press; the profession of journalism: she is reticent when it comes to members of the fourth estate
[originally used humorously in various contexts; its first usage with reference to the press has been attributed to Edmund Burke but this remains unconfirmed]

the fourth wall

the space which separates a performer or performance from an audience.
the conceptual barrier between any fictional work and its viewers or readers: he breaks the fourth wall by having Sam refer to the script and the play he’s acting in
[originally used of the proscenium opening in a theatre through which the audience sees the action of a play]

Do not confuse fourth with forth. Fourth means 'number four in a sequence' ( the fourth and fifth centuries), while forth means 'away from a starting point' ( the plant put forth new shoots).