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)

愛顧[aiko] patronage
一顧[ikko] (take no) notice of
恩顧[onko] favour
家庭を顧みない[kateiwokaeriminai] thinking little of one's family
回顧[kaiko] recollection

回顧録[kaikoroku] memoirs
軍事顧問[gunjikomon] military adviser
顧る[kaerimiru] to look back (e.g. over shoulder or at the past)
顧問[komon] adviser
顧慮[koryo] concern