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1. coming after the second and preceding the fourth in numbering or counting order, position, time, etc.; being the ordinal number of three: often written 3rd
2. denoting the third from lowest forward ratio of a gearbox in a motor vehicle
a. one of three equal or nearly equal parts of an object, quantity, etc.
b. (as modifier): a third part
4. the fraction equal to one divided by three (1/3)
5. the forward ratio above second of a gearbox in a motor vehicle. In some vehicles it is the top gear
a. the interval between one note and another three notes away from it counting inclusively along the diatonic scale
b. one of two notes constituting such an interval in relation to the other
7. Brit an honours degree of the third and usually the lowest class
8. goods of a standard lower than that of seconds
a unit of time equal to 1/60 of a second. The unit is seldom used. In modern physics, small intervals of time are usually expressed in decimal fractions of a second: milliseconds (10–3sec), microseconds (10–6sec), and nanoseconds (10–9 sec).