Pertaining to, or originated by, some person named Gregory, especially one of the popes of that name. Gregorian calendar, the calendar as reformed by pope Gregory XIII. In 1582, including the method of adjusting the leap years so as to harmonize the civil year with the solar, and also the regulation of the time of Easter and the movable feasts by means of epochs. See gregorian year (below).
(Science: medicine) gregorian chant, a form of reflecting telescope, named from Prof. James Gregory, of Edinburgh, who perfected it in 1663. A small concave mirror in the axis of this telescope, having its focus coincident with that of the large reflector, transmits the light received from the latter back through a hole in its center to the eyepiece placed behind it. Gregorian year, the year as now reckoned according to the gregorian calendar. Thus, every year, of the current reckoning, which is divisible by 4, except those divisible by 100 aud not by 400, has 366 days; all other years have 365 days. See bissextile, and note under style.