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

煎海鼠[iriko] dried sea slug
煎じる[senjiru] to boil
煎じ詰める[senjitsumeru] to boil down
煎じ詰めると[senjitsumeruto] after all
煎じ出す[senjidasu] to extract by broiling

煎じ薬[senjigusuri] (medical) decoction
煎じ立て[senjitate] freshly-drawn (tea)
煎りつく[iritsuku] to be scorched
煎り付ける[iritsukeru] to parch

助番[sukeban] leader of a female gang
ブロック番号[burokkubangou] block number
暗唱番号[anshoubangou] personal identification number
一貫番号[ikkanbangou] serial number
一番[ichiban] best

一番[hitotsugai] pair
一番鶏[ichibandori] first cockcrowing
一番手[ichibante] first player
一番乗り[ichibannori] leader of a charge
一番線[ichibansen] track no. 1