1. A political party organized in opposition to the major parties in a two-party system.
2. Someone other than the principals who are involved in a transaction.
1. Following the second position in an ordering or series:
2. The musical interval between one note and another three notes away from it
In music, an interval of three diatonic notes.
A third is an “imperfect interval” (having “major” and “minor” variants). A major third consists of four semitones (for example, c–e). A minor third consists of three semitones (c–e flat).