River
Ria
R. Dornhaus has written: 'Narrow-gap semiconductors' -- subject(s): Narrow gap semiconductors
Ria
a synonym for slow beginning with the letter r is retard
A. R. Channel has written: 'Jungle rescue' -- subject(s): Adventure and adventurers, Fiction, Jungles
English channel
David R. Montgomery has written: 'Channel classification, prediction of channel response, and assessment of channel condition' -- subject(s): Channels (Hydraulic engineering)
The name of a full turn, beginning with the letter "r", would probably be rotation.
ria
Rochester!
a ring?
rayon