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

瓜二つ[urifutatsu] as alike as two melons (two peas in a pod)
天糸瓜[hechima] sponge gourd
水瓜[suika] watermelon
破瓜[haka] age 16 (girl)
破瓜病[hakabyou] hebephrenia (disorganized schizophrenia) (disorganised)

木瓜[boke] (Chinese) flowering quince
南瓜[kabocha] pumpkin
黄瓜[kyuuri] cucumber
天瓜粉[tenkafun] talcum powder