the third letter of the Greek alphabet (?, ?).

the consonant sound represented by this letter.

the third in a series of items.

( initial capital letter ) Astronomy . a star that is usually the third brightest of a constellation

The third brightest star in the Southern Cross is Gamma Crucis.

a unit of weight equal to one microgram.

Physics . a unit of magnetic field strength, equal to 10? 5 gauss.

Photography . a measure of the degree of development of a negative or print.

Television . an analogous numerical indication of the degree of contrast between light and dark in the reproduction of an image in television.

Chiefly British . a grade showing that an individual student is in the third, or lowest, of three scholastic sections in a class. Compare alpha ( def. 7 ) , beta ( def. 8 ) .