varec

from The Century Dictionary.

• noun An impure sodium carbonate made in Brittany: it corresponds to the English kelp. Brande and Cox.
• noun In the original Freuch use of this word it applies to the seaweed itself before burning, but it is now commonly applied to the ash which results from the burning, utilized for the extraction from it of iodine and salts of potassium, as formerly of sodium carbonate. Also vareck.

from the GNU version of the Collaborative International Dictionary of English.

• noun The calcined ashes of any coarse seaweed used for the manufacture of soda and iodine; also, the seaweed itself; fucus; wrack.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The calcined ashes of any coarse seaweed used for the manufacture of soda and iodine.
• noun The seaweed itself; fucus; wrack.