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

弄り回す[ijirimawasu] to tinker with
どさ回りをやる[dosamawariwoyaru] to go on tour
螺子回し[nejimawashi] screwdriver
ウイック回転[uikkukaiten] Wick rotation
挨拶回り[aisatsumawari] courtesy call

一回[ikkai] once
ひと回り[hitomawari] one turn
一回忌[ikkaiki] first death anniversary
一回戦[ikkaisen] first game
一回分[ikkaibun] dose