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

お手伝いさん[otetsudaisan] maid
シリアル伝送[shiriarudensou] serial transmission
以心伝心[ishindenshin] telepathy
遺伝[iden] heredity
遺伝暗号[idenangou] genetic code

遺伝因子組替え[ideninshikumikae] recombinant gene splicing
遺伝学[idengaku] genetics
遺伝子[idenshi] gene
遺伝子工学[idenshikougaku] genetic engineering
遺伝情報[idenjouhou] genetic information

雨子[amago] land-locked variety of red-spotted masu trout (Oncorhynchus masou ishikawae)
御菓子[okashi] confections
お子さん[okosan] (someone else's) child
お子様[okosama] child (someone else's)
山梔子[kuchinashi] Cape jasmine (Gardenia jasminoides)

させ子[saseko] whore
梃子摺る[tekozuru] to have much trouble
螺子回し[nejimawashi] screwdriver
硝子[garasu] glass
獅子女[sufinkusu] sphinx

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

遺愛[iai] bequest
遺影[iei] portrait of deceased person
遺詠[iei] posthumous song or poem
遺家族[ikazoku] bereaved family
遺誡[ikai] one's last caution

遺骸[igai] remains
遺憾[ikan] regrettable
遺業[igyou] work left at death
遺訓[ikun] dying instructions
遺賢[iken] able men left out of office

御雑煮[ozouni] New Year dish
ファッション雑誌[fasshonzasshi] fashion magazine
悪口雑言[akkouzougon] all kinds of malicious gossip
雑える[majieru] to mix
雑ぜる[mazeru] to mix

混雑[konzatsu] confusion
錯雑[sakuzatsu] complication
雑音[zatsuon] noise (jarring, grating)
雑貨[zakka] miscellaneous goods