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).
December 21, 2012, at 6:12 am EST starts the first day of winter 2012/2013 (often just listed as winter 2012). Winter 2013/2014 (winter 2013) would begin on December 21, 2013, at 12:11 pm EST. In astronomy, each year in the Northern Hemisphere can be defined as beginning with the spring (vernal) equinox in March.