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).
How you define the first day of winter depends on whether you are referring to the astronomical or meteorological winter. The day in our calendar that marks the first day of winter usually refers to the astronomical seasons which are a result of the Earth's axis and orbit around the sun. However, at the Met Office we often use a meteorological definition of the seasons. Let's take a brief overview of the difference.