angle

The angle between two half-lines terminating at the same point is the ratio of the
length of the included arc of the circle (with its centre at that point) to the radius
of the circle. Symbols: ,, ... This is a quantity of dimension one with the SI unit radian
(), but very often degrees of arc are used.

Source:

PAC, 1996, *68*, 957*
(Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations
1996))
* on page 961