The Etymologies of the 1930s had N. uil “seaweed” under the root ᴹ√UY, along with a longer form N. oeruil “seaweed” where the initial element was N. oer “sea” (Ety/UY).

Neo-Sindarin: In Tolkien’s later writings, the word for “sea” was typically gaear (or gaer in compounds), so I would update the longer form to ᴺS. gaeruil for purposes of Neo-Sindarin, as suggested in Hiswelókë’s Sindarin Dictionary (HSD).