まっ四角[masshikaku] square
一天四海[ittenshikai] the world
下四半期[shimoshihanki] last quarter (of the year)
弦楽四重奏曲[gengakushijuusoukyoku] string quartet
再三再四[saisansaishi] repeatedly

三寒四温[sankanshion] alternation of three cold and four warm days
四つ[yottsu] four
四つんばい[yotsunbai] (crawl) on all fours
四つ角[yotsukado] four corners
四つ足[yotsuashi] four-footed (animal)

悪球[akkyuu] hard ball to hit
逸球[ikkyuu] muffed ball
衛星地球局[eiseichikyuukyoku] (satellite) earth station
眼球[gankyuu] eyeball
気球[kikyuu] balloon

球戯[kyuugi] billiards
球技[kyuugi] ball game (e.g. baseball, tennis, soccer)
球菌[kyuukin] coccus
球形[kyuukei] globular or spherical shape