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

一筋道[hitosujimichi] straight road
一筋繩[hitosujinawa] (piece of) rope
横筋[yokosuji] transversal
家筋[iesuji] lineage
括約筋[katsuyakukin] sphincter

筋違い[sujichigai] cramp
筋違い[sujikai] diagonal
筋骨[kinkotsu] muscles (sinews) and bones
筋書[sujigaki] synopsis

データの先頭[deetanosentou] beginning of data
一頭[ittou] one large animal (horses, cattle, etc.)
一頭立て[ittoudate] one-horse (carriage)
咽頭[intou] pharynx
駅頭[ekitou] station

音頭[ondo] leading a group of people
会頭[kaitou] society president
街頭[gaitou] in the street
核弾頭[kakudantou] nuclear warhead
巻頭[kantou] opening page of book