* Quarantine: A state of enforced isolation to prevent the spread of disease.
* Quarrel: A disagreement, an argument.
* Quarterly: Happening every three months.
* Quarter: One fourth of something, or a coin worth 25 cents.
* Quartet: A group of four singers or musicians.
* Quartz: A hard, crystalline mineral.
* Quart: A unit of liquid measurement, equal to one-fourth of a gallon.
* Quartan: A type of malaria with recurring fever every 72 hours.
Let me know if you'd like more examples!