| Zirkumfix | circumfix |
| Zirkumflex | circumflex |
| Zirkular | circular letter |
| zirkumbinär | circumbinary |
| Zirkus | circus |
| Zierkürbis | decorative gourd |
| Zirkumzision | circumcision |
| Zirmet | hartwort |
| zirka | approximate |
| Zirkel | compass pair of compasses circle |
| Zirkon | zircon |
| Zirkonium | zirconium |
| Zirkulation | circulation |
| Zirrus | cirrus |
| zirkadian | circadian |
| zirkumpolar | circumpolar |
| Irkutsk | Irkutsk |
| Wirkung | effect impact |
| Kurkume | turmeric |
| Borkum | Borkum |