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

御兄さん[oniisan] older brother
御兄ちゃん[oniichan] familiar form of "older brother"
御兄弟[gokyoudai] siblings
家兄[kakei] (my) elder brother
雅兄[gakei] polite word in letter to friend

義兄[gikei] brother-in-law
兄さん[niisan] older brother
兄嫁[aniyome] elder brother's wife
兄貴[aniki] one's senior

義妹[gimai] sister-in-law (younger)
兄妹げんか[kyoudaigenka] quarrel between siblings
吾妹子[wagimoko] my wife
吾妹[wagimo] my wife
姉妹会社[shimaigaisha] affiliated companies

姉妹都市[shimaitoshi] sister cities
従姉妹[itoko] cousin (female)
従妹[juumai] cousin (younger female)
弟妹[teimai] younger brother and sister
乳姉妹[chikyoudai] foster brother or sister

パートタイム従業員[paatotaimujuugyouin] part time employee
フルタイム従業員[furutaimujuugyouin] full-time employee
阿諛追従[ayutsuishou] excessive flattery
家従[kajuu] steward
郷に入っては郷に従え[gouniittehagounishitagae] when in Rome, do as the Romans do

屈従[kutsujuu] servile submission
合従連衡[gasshourenkou] alliance (of the Six Kingdoms against the Qin dynasty, and of individual Kingdoms with the Qin dynasty)
再従兄[saijuukei] elder second cousin
再従弟[saijuutei] younger second cousin
侍従[jijuu] chamberlain