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

鍬入れ式[kuwaireshiki] ground-breaking ceremony
オギノ式[oginoshiki] Ogino method
サイクルアンドライド方式[saikuruandoraidohoushiki] cycle and ride system
シーアンドエア方式[shiiandoeahoushiki] sea and air system
シーリング方式[shiiringuhoushiki] ceiling system

シップエア方式[shippueahoushiki] ship air system
スキャンロン方式[sukyanronhoushiki] Scanlon plan
違式[ishiki] informality
一括式[ikkatsushiki] batch mode
一式[isshiki] complete set

アルファ線[arufasen] alpha rays
エックス線[ekkususen] X-ray
サイン曲線[sainkyokusen] sinusoid
スピード線[supiidosen] speed lines
緯線[isen] parallel

一次線輪[ichijisenrin] primary coil
一線[issen] line
一直線[icchokusen] straight line
一番線[ichibansen] track no. 1
一塁線[ichiruisen] first-base line