ちょっと一杯[chottoippai] let's have a quick drink
ばつ一[batsuichi] being once divorced
一向[hitaburu] nothing but
サラダ一皿[saradahitosara] plate of salad

安全第一[anzendaiichi] safety first
一か八か[ichikabachika] sink or swim
一っ走り[hitoppashiri] spin (as in 'take a car for a spin')
一つ一つ[hitotsuhitotsu] one-by-one

一門[ichimon] family
陰門[inmon] (female) genitalia
開門[kaimon] opening gate
凱旋門[gaisenmon] arch of triumph
冠木門[kabukimon] gate with a crossbar

関門[kanmon] barrier
玉門[gyokumon] beautifully decorated gate (euph. for female genitalia)
桑門[soumon] monk
軍門[gunmon] camp gate