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

ストックホルム症候群[sutokkuhorumushoukougun] Stockholm syndrome
亜群[agun] subgroup
一群[ichigun] group
一群れ[hitomure] group
可換群[kakangun] Abelian group

魚群[gyogun] school of fish
繰込み群[kurikomigun] renormalisation group (physics)
群がる[muragaru] to swarm
群れ[mure] group