half dozen vs sixth

half dozen

• A set of six. 

sixth

• One of six equal parts of a whole. 

• The interval between one note and another, five notes higher in the scale, for example C to A, a major sixth, or C to A flat, a minor sixth. (Note that the interval covers six notes counting inclusively, for example C-D-E-F-G-A.) 

• The person or thing in the sixth position. 

• to divide by six, which also means multiplying a denominator by six 

• The ordinal form of the number six.