Definition of open sea
1 : the part of the sea not enclosed between headlands or included in narrow straits : the main sea
2 : the part of the sea outside the territorial jurisdiction or maritime belt of any country — compare mare clausum
Start your free trial today and get unlimited access to America's largest dictionary, with:
- More than 250,000 words that aren't in our free dictionary
- Expanded definitions, etymologies, and usage notes
- Advanced search features
- Ad free!
Seen and Heard
What made you want to look up open sea? Please tell us where you read or heard it (including the quote, if possible).