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

へし折る[heshioru] to smash
一折り[hitoori] one box
右折[usetsu] turning to the right
右折禁止[usetsukinshi] No Right Turn!
我を折る[gawooru] to concede a point

解折[kaiseki] analysis
回折[kaisetsu] diffraction
回折格子[kaisetsukoushi] (diffraction) grating
曲折[kyokusetsu] windings
九折[kyuusetsu] many turns (in a road)