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)

夏季休暇[kakikyuuka] summer vacation
季刊[kikan] quarterly (e.g. magazine)
季語[kigo] seasonal word (in haiku)
季候[kikou] season
季節[kisetsu] season

季節はずれ[kisetsuhazure] unseasonable
季節的[kisetsuteki] seasonal
季節風[kisetsufuu] seasonal winds
四季[shiki] four seasons
冬季[touki] (season of) winter

マルコフ遷移[marukofuseni] Markov transition
移す[utsusu] to change
移り気[utsurigi] whim
移りゆく[utsuriyuku] to change
移り香[utsuriga] lingering scent

移り変り[utsurikawari] change (e.g. season)
移る[utsuru] to move (house)
移ろう[utsurou] to change (with the passage of time)
移管[ikan] transfer of control
移行[ikou] switching over to