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

鬼利死丹[kirishitan] early Japanese Christianity (from the later Muromachi period)
あっ死[asshi] crushing to death
安楽死[anrakushi] euthanasia
一死[isshi] dying
一死後[isshigo] after one out (in Baseball)

一死報国[isshihoukoku] dying for one's country
煙死[enshi] death by smoke suffocation
横死[oushi] violent (tragic or accidental) death
仮死[kashi] asphyxiation
過労死[karoushi] death from overwork and mental stress