prerhotic

adjective1

1. •
   (rare) Occurring before the letter ⟨r⟩ or before any one of the sounds that letter tends to represent (e.g., [r], [ɽ], [ɹ], [ɻ], [ʀ], [ʁ], etc.).

   • 1993 Summer, Ralph H. Emerson, “The Distribution of Eighteenth-Century Prerhotic O-Phonemes in Walker’s Critical Pronouncing Dictionary” in American Speech LXVIII, № 2, pages 115–138 — 1993