Definition of opponent for English Language Learners. : 1  a person, team, group, etc., that is competing against another in a contest. : 2  a person, group, etc., that is against something (such as an action, law, or system) : someone or something that does not want something to exist, be done, etc.
On the Celtic calendar, the traditional first day of winter is 1 November (Samhain, the Celtic origin of Halloween); spring starts 1 February (Imbolc, the Celtic origin of Groundhog Day); summer begins 1 May (Beltane, the Celtic origin of May Day); the first day of autumn is 1 August (Celtic Lughnasadh).
Astronomical and solar reckoning. In some cultures in the Northern Hemisphere (e.g. Germany), the astronomical Vernal equinox (varying between 19 and 21 March) is taken to mark the first day of spring, and the Summer solstice (around 21 June) is taken as the first day of summer.