RIDGELING is a 9 letter word that starts with R.
\Ridge"ling\, n. [Prov. E. riggilt, riggot, ananimal half castrated, a sheep having only one testicle; cf. Prov. G. rigel, rig, a barrow hog, rigler a cock half castrated.] (Zo["o]l.) A half-castrated male animal.
WordNet Dictionary