third

Concise Oxford English Dictionary © 2008 Oxford University Press:
third/θɜːd/

▶ordinal number

• 1 constituting number three in a sequence; 3rd.

• 2 (a third/one third) each of three equal parts into which something is or may be divided.

• 3 Music an interval spanning three consecutive notes in a diatonic scale, e.g. C to E (major third, equal to two tones) or A to C (minor third, equal to a tone and a semitone).

  ■ Music the note which is higher by this interval than the tonic of a diatonic scale or root of a chord.

• 4 Brit. a place in the third grade in an examination for a university degree.

– phrases
the third estate the third order or class in a country or society, comprising the common people.
third time lucky (or US third time is the charm) used to express the hope that one may succeed in the third attempt.

– derivatives
thirdly adverb.

– origin OE thridda, of Gmc origin; rel. to three.