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

山梔子[kuchinashi] Cape jasmine (Gardenia jasminoides)
悪巫山戯[warufuzake] prank
安土桃山時代[azuchimomoyamajidai] Azuchi-Momoyama period (approx. 1558-1600 CE)
案山子[kakashi] scarecrow
奥山[okuyama] remote mountain

岡山県[okayamaken] Okayama prefecture (Chuugoku area)
下山[gezan] descending (mountain)
夏山[natsuyama] summery mountain
火山[kazan] volcano
火山灰[kazanbai] volcanic ash