三日三夜
みっかみよ 3 days and 3 nights

三日三晩
みっかみばん 3 days and 3 nights

三日坊主
みっかぼうず one who can stick to nothing unsteady worker

三日天下
みっかてんか a short-lived rule being in power only for a brief period brief championship

三日月
みかづき みかずき new moon crescent moon

三日月形
みかづきけい crescent shape

三日路
みっかじ three-day journey

三日間
みっかかん three days