一も二も無く[ichimonimonaku] unhesitatingly
一言二言[hitokotofutakoto] a word or two
一石二鳥[issekinichou] killing two birds with one stone
一二に及ばず[ichininioyobazu] right away
一姫二太郎[ichihimenitarou] It's good to have a girl first and then a boy

うり二つ[urifutatsu] as alike as two melons (two peas in a pod)
黄道十二宮[koudoujuunikyuu] twelve signs of the zodiac
二度[futatabi] again
最小二乗法[saishounijouhou] least-squares method
三十二分音符[sanjuunibuonpu] 32nd note

一週[isshuu] one week
一週間[isshuukan] one week
今週[konshuu] this week
今週中に[konshuujuuni] before the week is out
さ来週[saraishuu] week after next

七週の祭[nanamawarinoiwai] the Feast of Weeks
七週の祭り[nanashuunomatsuri] the Feast of Weeks
週刊[shuukan] published weekly
週刊雑誌[shuukanzasshi] weekly magazine

あっとゆう間に[attoiumani] just like that
此間[konaida] the other day
此の間[konokan] the other day
間誤付かせる[magotsukaseru] to fluster
間誤付く[magotsuku] to be confused

クローン人間[kuroonningen] (human) clone
シゾイド人間[shizoidoningen] schizoid person
ベクトル空間[bekutorukuukan] vector space
π中間子[paichuukanshi] pi meson
位相空間[isoukuukan] phase space (physics)