One, especially a politician, who is guided by personal advantage rather than by consistent, respectable principles.
Etymology: 19th-century American English. Possibly from snallygaster, a mythical beast that preys on poultry and children, possibly from Pennsylvania German schnelle geeschter, from German schnell, quick + geist, spirit.
Today I learned this word. It seems a coincidence, but afterwards I read that a minister from my country dared to say on his facebook that some of his critics should be slapped on the face. Where has the "culture" of good manners gone to?