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

カバー曲[kabaakyoku] remake of another artist's song (a "cover")
サイン曲線[sainkyokusen] sinusoid
愛唱曲[aishoukyoku] favourite song
委曲[ikyoku] details
一曲[ikkyoku] tune (melody, piece of music)

迂曲[ukyoku] meander
円曲[enkyoku] roundabout way (of speaking or working)
円錐曲線[ensuikyokusen] conic curve
円舞曲[enbukyoku] waltz (composition)
演曲[enkyoku] musical program

ゼロ次[zeroji] zero-order
位次[iji] order of rank
一次[ichiji] first
一次記憶[ichijikioku] first memory
一次元[ichijigen] one dimensional

一次線輪[ichijisenrin] primary coil
一次電流[ichijidenryuu] primary current
月次[tsukinami] every month
五十三次[gojuusantsugi] the 53 Toukaidou stages
高次[kouji] higher-order-

その反面[sonohanmen] on the other hand
委細面談[isaimendan] details when I see you
一面[ichimen] one face
一面観[ichimenkan] one-sided view
一面識[ichimenshiki] (a) passing acquaintance

隠面[inmen] hidden surface
右面[umen] right side
液面[ekimen] liquid surface
凹面[oumen] concavity
凹面鏡[oumenkyou] concave mirror