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)

一段[ichidan] more
一段動詞[ichidandoushi] ichidan verb (one of the two main conjugation classes of verbs in modern Japanese, usually ending in -eru or -iru)
一段落[ichidanraku] completing the first stage
階段[kaidan] stairs
格段[kakudan] special

計画段階[keikakudankai] planning stage
決済手段[kessaishudan] method of payment
減段[gentan] reduction (of crop size)
五段[godan] Japanese verb group
五段動詞[godandoushi] godan verb (one of the two main conjugation classes of verbs in modern Japanese, usually ending in -u, -ku, -su, -tsu, -gu, -bu, -mu, etc.)

一般生活[ippanseikatsu] everyday life
隠退生活[intaiseikatsu] secluded life
火山活動[kazankatsudou] volcanic activity
快活[kaikatsu] cheerful
活火山[kakkazan] active volcano

活気[kakki] energy
活況[kakkyou] activity
活劇[katsugeki] action picture
活字[katsuji] printing type
活字体[katsujitai] printed form (of writing)

コンピューター援用生産[konpyuutaaenyouseisan] computer-aided manufacture
コンピューター援用設計[konpyuutaaenyousekkei] computer-aided design
コンピュータ用語[konpyuutayougo] computerese
スキー用品[sukiiyouhin] ski outfit
愛用[aiyou] favorite

悪用[akuyou] abuse
医学用語[igakuyougo] medical term
医用[iyou] medical use
医療用[iryouyou] medical use
一人用[hitoriyou] for one person's use