\Fu"cus\, n.; pl. {Fuci}. [L. rock lichen, orchil, used as
a red dye, red or purple color, disguise, deceit.]
1. A paint; a dye; also, false show. [Obs.]

2. (Bot.) A genus of tough, leathery seaweeds, usually of a
   dull brownish green color; rockweed.

Note: Formerly most marine alg? were called fuci.