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

彼の人[anohito] he
殆どの人[hotondonohito] most people
アメリカ人[amerikajin] American person
クローン人間[kuroonningen] (human) clone
シゾイド人間[shizoidoningen] schizoid person

ドイツ人[doitsujin] German person
ベトナム人[betonamujin] Vietnamese (person)
ペルシア人[perushiajin] Persian person
ユダヤ人[yudayajin] Jew
愛人[aijin] lover

亜種[ashu] subspecies
異機種[ikishu] heterogenous equipment
異種[ishu] different kind (species, variety)
育種[ikushu] (plant) breeding
育種家[ikushuka] (plant) breeder

育種所[ikushujo] (plant) nursery
一種[isshu] species
一粒種[hitotsubudane] an only child
種違い[tanechigai] half-brother
艶種[tsuyadane] love affair