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

ト音記号[toonkigou] G clef
ドル記号[dorukigou] dollar sign ($)
ハ音記号[haonkigou] C clef
ブレーク信号[bureekushingou] break signal
ブロック番号[burokkubangou] block number

ヘ音記号[heonkigou] F clef
哀号[aigou] moan
暗号[angou] code
暗号化[angouka] encryption
暗号化手法[angoukashuhou] cryptography