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

グループ分離キャラクタ[guruupubunrikyarakuta] group separator
システム分析[shisutemubunseki] systems analysis
ファイル分離キャラクタ[fairubunrikyarakuta] file separator
ユニット分離キャラクタ[yunittobunrikyarakuta] unit separator
レコード分離キャラクタ[rekoodobunrikyarakuta] record separator

異分子[ibunshi] outsider
医薬分業[iyakubungyou] separation of medical and dispensary practice (practise)
一回分[ikkaibun] dose
一部分[ichibubun] part
一分[ichibu] one tenth