'sea-green' is a compound formed in English from the words 'sea' and 'green'; 'sea' (Old English 'sǣ') referred to the sea and 'green' (Old English 'grēne') referred to the color green.

'sea' and 'green' both come from Old English ('sǣ' and 'grēne'); the compound form 'sea-green' developed in later English (Middle to Early Modern English) as a descriptive color name and stabilized in Modern English as a color term.

Initially a literal combination meaning 'green of the sea' or 'green like the sea'; over time it became standardized as the name of a specific greenish-blue color (sea-green).