(a.) Of or pertaining to the seasons.

aestival alternate arctic autumn autumnal beating boreal brumal canicular circling cyclic epochal equinoctial even every other hibernal hiemal intermittent isochronal measured metronomic midsummer midwinter oscillatory out of season periodical pulsing reciprocal recurrent recurring rhythmic rotary serial solstitial spring springlike steady summer summerlike summerly summery undulant undulatory vernal wavelike wheeling winter winterlike wintery wintry