conk
n.— «Often the first thing that is observed is what is called a conk—this is a diagnostic sign. The conk starts as a button-like growth that forms near the base of the trunk. This mushroom manifestation eventually changes into a shelf fungi; half-moon in shape and up to 8 inches wide and 2 inches thick.» —“Fairly common Ganoderma butt rot affects palms” by Ralph Mitchell Sun-Herald (Florida) Sept. 10, 2006. (source: Double-Tongued Dictionary)