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

安全第一[anzendaiichi] safety first
及第[kyuudai] passing an examination
及第者[kyuudaisha] successful examinee
及第点[kyuudaiten] passing mark
次第[shidai] dependent upon

次第に[shidaini] gradually (progress into a state)
次第書き[shidaigaki] printed program
式次第[shikishidai] program of a ceremony (programme)
手当たり次第[teatarishidai] using anything one can lay one's hands on
出来次第[dekishidai] as soon as completed

暗部[anbu] dark side (of nature, town, etc.)
鞍部[anbu] col
医学部[igakubu] medical faculty
一局部[ichikyokubu] one part
一部[ichibu] one part

一部始終[ichibushijuu] full particulars
一部分[ichibubun] part
陰部[inbu] the genital area
営業部[eigyoubu] sales department
掩護部隊[engobutai] covering force

イ長調[ichouchou] A major
データビット長[deetabittochou] data bit length
ト長調[tochouchou] G major
ニ長調[nichouchou] D major
ハ長調[hachouchou] C major

ヘ長調[hechouchou] F major
ホ長調[hochouchou] E major
ロ長調[rochouchou] B major
委員長[iinchou] committee chairman
意味深長[imishinchou] with profound (often hidden) meaning