Numbers:
* Deca-: The prefix itself signifies ten.
* Decade: A period of ten years.
* Decameter: A unit of length equal to 10 meters.
* Decagram: A unit of mass equal to 10 grams.
* Decaliter: A unit of volume equal to 10 liters.
* Decathlon: An athletic contest consisting of ten events.
* Decalogue: The Ten Commandments.
Other words:
* Decadence: A state of moral or cultural decline.
* Deciduous: Falling off, especially leaves of trees.
* Decimate: To kill or destroy a large proportion of.
* Decipher: To decode or interpret.
These are just a few examples. Many other words use "deca" as a prefix to indicate a quantity of ten.