Directly related to "tenth":
* Decimal: A number system based on ten.
* Decimate: To kill one in ten, originally, now meaning to destroy a large part of something.
* Decile: Each of the ten groups into which a population can be divided, ranked in order of some variable.
Other words with related meanings:
* Decade: A period of ten years.
* Decameron: A collection of 100 stories told by ten people over ten days, written by Boccaccio.
* Decimeter: A metric unit of length, equal to one tenth of a meter.
* Decimation: The act of killing one in ten.
* Decimate: To kill or destroy a large part of something.
Note: While "decima" is the root, the actual spelling of words can vary, with "decem" being used instead of "decima" sometimes.