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

弐拾[nijuu] twenty
弐心[nishin] duplicity

弐つ[futatsu] two (used in old or legal documents)

この先の心持ち[konosakinokokoromochi] feelings from this point on
御心配なく[goshinpainaku] don't worry
愛郷心[aikyoushin] love of one's hometown
愛国心[aikokushin] patriotic feelings
悪心[akushin] evil thought

悪心[oshin] nausea
安心[anshin] relief
安心立命[anshinritsumei] spiritual peace and enlightenment
以心伝心[ishindenshin] telepathy
依頼心[iraishin] spirit of dependence