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

アラビア数字[arabiasuuji] Arabic numeral
キリル文字[kirirumoji] Cyrillic character
ギリシア文字[girishiamoji] Greek character
羅馬字[roomaji] Latin alphabet
ロシア文字[roshiamoji] Russian character

異体字[itaiji] kanji variants
一字[ichiji] letter
一字千金[ichijisenkin] word of great value
一丁字[itteiji] single letter or character
一文字[ichimonji] straight line