The precise sense and etymology of this hapax remain unclear, though an association with later English ray n.10 (‘Diarrhoea, esp. in sheep or cattle’) seems possible. The context suggests that the word refers to a type of disease in horses.
s.
1zool.horsespathol.disease of horses, possibly ray or a form of diarrhoea (?):
(
s.xiiiin; MS: s.xiii
)
Se vos trovez en une piere un cheval entaillié ki est apelez Pegasus [...] si garist le cheval ki la porte del raier et de totes enfermetez
291.XXIII.4