January UK /ˈd͡ʒæn.jʊ.ə.ɹi/US /ˈd͡ʒæn.juˌɛɹi/noun 1forms 2phrases 1 noun1 •The first month of the Gregorian calendar, following the December of the previous year and preceding February.01/01/09 : Thursday, 1st January(,) 2009.American style: Thursday, January 1st, 2009. formsJanuaries · Januarys Phrases with January Dry JanuaryA popular health challenge where a person abstains from alcohol for the entire month of January.