Here are some words with that root:
* Marine: relating to the sea
* Maritime: relating to the sea or navigation
* Mariner: a sailor
* Submarine: a vessel that travels underwater
* Mariculture: the cultivation of marine organisms
* Marigram: a record of tidal changes
* Mariner's compass: a device used for navigation
* Marigold: a type of flower (the name is thought to come from "Mary's gold" and not directly related to the sea)
Let me know if you'd like more examples!