x1 is Spring time/vernal [warming season] in the northern hemisphere and Autumn/autumnal [cooling season] in the southern hemisphere of year x2 and for celestial body x3.
This word unifies opposite seasons so that one can more easily reference something like "the (northern) vernal equinox" without having to specify hemisphere, nor without having to specify two different descriptions for the same point in time. One can now say "Yuri's Night begins in the northern Spring and southern Autumn" without difficulty and without making it sound like it might depend on location or happen multiple times per year. See also: "vensa", "critu", "crisaunra", "critoinsa", "dunraisa".