I. abbreviation
1. rabbi
2. radial
3. radical — used especially of a monovalent hydrocarbon radical
4. Rankine
5. Reaumur
6. recipe
7. registered trademark — often enclosed in a circle
8. regular
9. Republican
10. river
11. R-value
II. certification mark
— used to certify that a motion picture is of such a nature that admission is restricted to persons over a specified age (as 17) unless accompanied by a parent or guardian; compare g , NC-17 , pg , PG-13