Gregorian calendar noun

The calendar reformed by Pope Gregory XIII in 1582

Gregorian chant or Gregorian tones noun

Plainsong, introduced by Pope Gregory I

Gregorian telescope noun

A reflecting telescope invented by James Gregory (1638–75)

Gregorian wig noun

A 16c or 17c type of wig attributed to a barber called Gregory

Gregory's mixture /gregˈər-iz/ or Gregory's powder noun (also called (informal) Gregˈory)

A laxative powder of rhubarb, magnesia and ginger, formulated by Dr James Gregory (1753–1821)