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

音叉[onsa] tuning fork
交叉[kousa] crossing
叉手網[sadeami] dip net
叉銃[sajuu] stacked arms
三叉[mitsumata] three-pronged (fork)

三叉路[sansaro] three-forked road
三仙叉[sansensa] trident dagger
指叉[sasumata] two-pronged weapon for catching a criminal
二叉[futamata] bifurcation