Definition of flathead:
(n) :
Any fish in the family Platycephalidae.
(n) :
(only "flatheads" as plural) A type of screw or bolt designed to fit in a countersink so that it sits flush with a surface.
(n) :
(only "flatheads" as plural) Synonym of side valve.
(n) :
Their Salishan language.
(n) :
One of the Salish people of Washington state and British Columbia.
(n) :
(US, informal) Ellipsis of flathead catfish [A large freshwater catfish native to North America, Pylodictis olivaris.]