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)

ケーソン工法[keesonkouhou] caisson method
シールド工法[shiirudokouhou] shield method
ロボット工学[robottokougaku] robotics
圧延工場[atsuenkoujou] rolling mill
遺伝子工学[idenshikougaku] genetic engineering

印刷工[insatsukou] pressman
化学工学[kagakukougaku] chemical engineering
化学工業[kagakukougyou] chemical industry
化成工業[kaseikougyou] chemical industry
加工[kakou] manufacturing