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

是等[korera] these
其等[sorera] those (near the second person)
等閑[naozari] neglect
悪平等[akubyoudou] misguided equality
位階勲等[ikaikuntou] court rank and honors

一等[ittou] first-class
１等軍曹[ittougunsou] sergeant first-class
１等国[ittoukoku] first-class power
１等車[ittousha] first-class carriage (coach)
１等賞[ittoushou] first place prize