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

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

ゼロ次[zeroji] zero-order
位次[iji] order of rank
一次[ichiji] first
一次記憶[ichijikioku] first memory
一次元[ichijigen] one dimensional

一次線輪[ichijisenrin] primary coil
一次電流[ichijidenryuu] primary current
月次[tsukinami] every month
五十三次[gojuusantsugi] the 53 Toukaidou stages
高次[kouji] higher-order-

一粒[hitotsubu] (a) grain
一粒子既約[ichiryuushikiyaku] one particle irreducible (physics)
一粒種[hitotsubudane] an only child
雨粒[amatsubu] raindrop
穀粒[kokuryuu] kernel

素粒子[soryuushi] elementary particle
素粒子加速器[soryuushikasokuki] particle accelerator
大粒[ootsubu] large grain
長粒米[chouryuumai] long grain rice
麦粒腫[bakuryuushu] sty (on the eyelid)