E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
High Seas.
All the sea which is not the property of a particular country. The sea three miles out belongs to the adjacent coast, and is called mare clausum. High-seas, like high-ways, means for the public use. In both cases the word high means “chief,” “principal.” (Latin, allum, “the main sea;” allus, “high.”)
