Coûter
Rien ne lui coûte = He sticks at nothing; He spares no trouble.
Coûte que coûte = Cost what it may.
Coûter les yeux de la tête = To cost a small fortune, a fearful lot of money.
Coutume
*Une fois n’est pas coutume = It is only this once; One swallow does not make a summer; Once does not count.
Coutumier
Il est coutumier du fait = It is not the first time he has done it.
Couture
Ils étaient battus à plate couture = They were beaten hollow.