Definition of "fucus"

Sea-weeds, consisting of different species of fuci, algæ, and confervæ, are much used as a manure on the sea-coasts of Britain and Ireland.

a. 1813, Sir Humphry Davy, "Lecture VI" in Elements of Agricultural Chemistry (1840 reprint)

One of the feeblest of these inlets, after winding for some time among buried fragments of masonry, and knots of sunburnt weeds whitened with webs of fucus, stays itself in an utterly stagnant pool beside a plot of greener grass covered with ground ivy and violets.

1853, John Ruskin, “Torcello”, in The Stones of Venice, volume II (The Sea-Stories), London: Smith, Elder, and Co., […], § I, page 11