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)

悪声[akusei] bad voice
雨声[usei] sound of rain
怨声[ensei] complaint
黄色い声[kiiroikoe] shrill voice
音声[onsei] voice

音声圧縮[onseiasshuku] voice compression
音声学[onseigaku] phonetics
仮声[kasei] falsetto
家声[kasei] honour of the family
蚊のささやくような声[kanosasayakuyounakoe] faint voice