Common words:
* Extra: (adjective) meaning more than usual or necessary.
* Extracurricular: (adjective) relating to activities that are not part of the regular school curriculum.
* Extraordinary: (adjective) very unusual or remarkable.
* Extravagant: (adjective) spending or costing a lot of money.
* Extract: (verb) to remove or take out something, especially by force
* Extraterrestrial: (adjective) relating to or coming from outside the Earth.
* Extrovert: (noun) a person who is outgoing and enjoys being with other people.
Less common words:
* Extradural: (adjective) situated outside the dura mater, the outermost membrane surrounding the brain and spinal cord.
* Extrapolate: (verb) to estimate something unknown from something known.
* Extramarital: (adjective) relating to or happening outside marriage.
* Extraneous: (adjective) not relevant or essential.
* Extraordinary: (adjective) very unusual or remarkable.
This is not an exhaustive list, but it gives you a good starting point. You can use a dictionary or thesaurus to find more words that start with the prefix "extra-."